Document:

THE DEBENTURE  REPRESENTED BY THIS CERTIFICATE HAS NOT BEEN REGISTERED UNDER THE
SECURITIES  ACT OF  1933,  AS  AMENDED  (THE  "SECURITIES  ACT")  OR  ANY  STATE
SECURITIES  LAWS,  AND NEITHER SUCH  DEBENTURES OR ANY INTERESTS  THEREIN MAY BE
OFFERED,  SOLD,  PLEDGED,   ASSIGNED  OR  OTHERWISE  TRANSFERRED  UNLESS  (I)  A
REGISTRATION  STATEMENT WITH RESPECT  THERETO IS EFFECTIVE  UNDER THE SECURITIES
ACT AND ANY APPLICABLE  STATE  SECURITIES  LAWS, OR (II) THE ISSUER  RECEIVES AN
OPINION OF COUNSEL TO THE HOLDER OF SUCH  DEBENTURE,  WHICH  COUNSEL AND OPINION
ARE REASONABLY  SATISFACTORY TO THE ISSUER,  THAT SUCH DEBENTURE MAY BE OFFERED,
SOLD,  PLEDGED,  ASSIGNED OR TRANSFERRED IN THE MANNER  CONTEMPLATED  WITHOUT AN
EFFECTIVE  REGISTRATION  STATEMENT UNDER THE SECURITIES ACT OR APPLICABLE  STATE
SECURITIES LAWS.

Number
R-001                                                                   $213,000

                           TOP AIR MANUFACTURING, INC.

             CONVERTIBLE SUBORDINATED DEBENTURE DUE JANUARY 15, 2005

         TOP AIR  MANUFACTURING,  INC.,  an  Iowa  corporation  (the  "Company")
promises to pay to S. Lee Kling, or registered assigns, the principal sum of Two
Hundred Thirteen Thousand Dollars, ($213,000) on January 15, 2005 (the "Maturity
Date"),  and  to  pay  interest  on  the  principal  amount  of  this  Debenture
semi-annually on July 15 and January 15 of each year; provided,  however that if
such date is not a Business Day,  then the Interest  Payment Date shall occur on
the first succeeding Business Day (collectively,  the "Interest Payment Dates"),
commencing  on July 15, 2000.  Interest on the unpaid  principal  balance  shall
accrue from the date hereof at a  fluctuating  rate per annum equal at all times
to one percent  (1%) per annum in excess of the Prime Rate,  with each change in
such  fluctuating   interest  rate  to  take  effect   simultaneously  with  the
corresponding change in the Prime Rate.

         This  Debenture  is  one  of  the  Company's  convertible  subordinated
debentures due 2005 (collectively,  the "Debentures") in the aggregate principal
amount of  $500,000  issued by the  Company in a private  placement  transaction
effected on January 25, 2000.  Certain defined terms used in this instrument are
set forth in paragraph 23 of this Debenture.

         Each of the  Debentures,  including this  Debenture,  is subject to the
following  terms:

         1. Payment.

         The  payment  of  interest  on  this  Debenture  shall  be made on each
Interest  Payment  Date to the Holder  hereof as of the close of business on the
first day of the month in which the subject  Interest  Payment  Date occurs (the
"Interest  Payment  Record Date"),  whether or not such Interest  Payment Record
Date  is a  Business  Day.  Payment  of the  principal  of and  interest  on the
Debentures  will be made at the  principal  office of the  Company or such other
place as may be  designated  by the  Company,  in such coin or  currency  of the
United  States of America as at the time of payment is legal  tender for payment
of public and private debts;  provided,  however,  that payment of principal and
interest  may be made,  at the  option of the  Company,  by check  mailed to the
address of the Holder of the Debentures (each a "Holder," and collectively,  the
"Holders")  entitled  thereto at such address as shall  appear on the  Debenture
records  maintained by the Company.  Interest payable will be paid to the Holder
in whose name the  Debentures  are registered as of the close of business on the
Interest  Payment Record Date which  corresponds to the Interest Payment Date in
question.

         2. Redemption.

         This Debenture is not subject to redemption  prior to January 15, 2002.
Thereafter,  the Debentures will be redeemable, at the option of the Company, at
any time in whole and from time to time in part at: (a) 105% of par from January
15, 2002 to January 15,  2003;  (b) 103% of par from January 15, 2003 to January
15, 2004;  and (c) from and after January 15, 2004,  at par, in each case,  plus
accrued interest.

         If less than all of the Debentures are to be redeemed, the Company will
select  Debentures  for such  partial  redemption  pro  rata or by lot,  and the
Company  may select  for  redemption  portions  of the  principal  amount of any
Debentures of a denomination  larger than $1,000.  In the event of redemption of
this Debenture in part only, a new Debenture(s) for the unredeemed portion shall
be issued in the name of the Holder upon the surrender hereof.

         The Company shall give notice of any redemption  permitted  pursuant to
this paragraph 2 by first class mail,  postage prepaid,  mailed not less than 30
nor  more  than 90 days  prior  to the  date  fixed  for  such  redemption  (the
"Redemption Date"), to each Holder of Debentures to be redeemed,  at the address
of such Holder  appearing in the Debenture  register and otherwise in the manner
prescribed in paragraph 14 hereof.  All such notices of  redemption  shall state
(i) the Redemption  Date, (ii) the Redemption  Price,  (iii) if less than all of
the  Debentures  are to be redeemed,  the  identification  (and,  in the case of
partial  redemption,  the principal  amount) of the particular  Debentures to be
redeemed,  (iv) that on the Redemption Date the Redemption Price will become due
and payable upon each such Debenture,  and that interest  thereon shall cease to
accrue on or after said date, and (v) the place or places where such  Debentures
are to be surrendered for payment of the Redemption Price.

         3. Subordination.

               (a) The indebtedness evidenced by this Debenture and other rights
of the Holder of this  Debenture  granted by or  arising  out of this  Debenture
shall be  unconditionally  subordinated  and  junior  in  priority  and rank and
subject in right of payment,  to the extent and in the manner  herein set forth,
to the prior payment in full of all Senior Debt (as hereinafter defined), and to
all of the liens,  security  interests  and other  rights of the  holders of the
Senior  Debt,  whether  existing on the date hereof or  hereafter  created.  The
subordination  of  priorities  and  all  other  aspects  of  the   subordination
provisions  contained  in this  paragraph  3 shall apply and be  effective:  (i)
regardless of the time or order of perfection or filing of security interests or
the time or order of  attachment  of security  interests,  (ii)  notwithstanding
anything to the contrary contained in the provisions of the Bankruptcy Code, the
Uniform  Commercial  Code in any relevant  statute of the United States,  or the
laws of the  State of Iowa or any  other  relevant  state  which  relate  to the
priority of liens,  security interests or mortgages,  and (iii)  notwithstanding
the lapse of perfection  of liens or security  interests of any holder of Senior
Debt or the  failure  of any  holder  of  Senior  Debt to  perfect  its liens or
security  interests.  "Senior Debt" shall mean the principal of (and premium, if
any), interest accrued or to be accrued, absolute or contingent obligations, and
obligations  acquired  by  purchase  or  otherwise,  as well  as all  reasonable
collection  costs and  attorneys'  fees  incurred  in  enforcing  any rights and
obligations, and all other obligations, liabilities or rights (and, in addition,
of the Company as a debtor-in-possession under any bankruptcy act or code, state
or federal law, common law or equitable doctrine,  and of any trustee,  receiver
or other  party  appointed  for the  Company  under  any such law,  doctrine  or
proceeding):  (A) under any indebtedness of the Company,  whether outstanding on
the date hereof or hereafter  created,  for money borrowed by or loaned to or on
behalf of the Company,  whether or not secured and whether or not the Company is
the  sole  or a  joint  obligor  thereof,  including  but not  limited  to,  any
obligation of the Company to any financial institution under any loan agreement,
instrument,  or letter of credit that has been or will be issued for the account
of the Company;  (B) under any obligations of the Company under any guarantee of
the Company,  whether existing on the date hereof or hereafter  created,  of any
payment  obligation  for money  borrowed by or loaned to any  Subsidiary  of the
Company, whether or not secured; (C) under any deferrals, renewals or extensions
of  any  such  indebtedness  or any  debentures,  notes  or  other  evidence  of
indebtedness  issued in exchange for such Senior  Debt;  and (D) with respect to
any costs, whether payable by way of enforcement or otherwise, which the holders
of the Senior Debt are entitled to be paid or recover.

               (b) (i) Subject to the provisions of clauses (ii), (iii) and (iv)
of this paragraph 3(b), the Company shall make all regularly  scheduled payments
on the Debentures  and all other payments in respect of any Optional  Redemption
of the Debentures  (including  premiums  thereon,  if any), so long as no Senior
Debt Default has occurred or would occur as a result of such payment.

                    (ii) In the  event of any  Senior  Debt  Default,  no amount
shall be paid by the Company in respect to any interest hereon, principal hereof
(whether at maturity by Optional  Redemption  or otherwise) or any other payment
obligation hereunder,  and the Holder of this Debenture shall not be entitled to
receive any amount,  in respect of this  Debenture  unless and until such Senior
Debt  Default  shall have been cured or waived or shall have ceased to exist and
any  acceleration  of Senior Debt  occurring as a result thereof shall have been
rescinded or annulled,  or the Senior Debt to which such default  relates  shall
have been paid in full.

                    (iii) In the event that any Senior Debt is declared  due and
payable  before its  maturity  date because of the  occurrence  of a Senior Debt
Default not cured within any applicable cure periods, the holders of such Senior
Debt shall be entitled to receive payment in full of such Senior Debt before the
Holder of this  Debenture  is  entitled to receive any payment on account of the
Debenture.

                    (iv) In the event of the  liquidation  of the Company or the
distribution  of any of its assets or the securities of any successor on account
of any liquidation, bankruptcy, receivership, reorganization, assignment for the
benefit of creditors or similar  proceeding,  the Holder of this Debenture shall
not be entitled to any payment or distribution on account of the Debenture until
all Senior Debt has been  satisfied  in full,  and the Holder of this  Debenture
shall receive any money,  securities or other  property  distributed in any such
proceeding  on account of the  Debenture in trust for the benefit of the holders
of the Senior  Debt and shall  deliver  any such  property to the holders of the
Senior  Debt in the same form as  received,  adding  only such  endorsements  or
assignments  as may be necessary,  for  application to the  satisfaction  of the
Senior Debt in such order as the holders of the Senior Debt in their  discretion
may determine.  Any excess of such property  remaining after satisfaction of all
of the  Senior  Debt  shall be  returned  to the  Holder  of this  Debenture  or
delivered  as  otherwise  ordered  by any court  having  jurisdiction  over such
proceedings.  The holders of the Senior Debt may liquidate any noncash  property
received from the Holder of this Debenture in the manner in which collateral may
be liquidated  under the terms of the Uniform  Commercial Code as enacted in the
State of Iowa and such  property may be liquidated in any order that the holders
of the Senior Debt shall determine in the exercise of their sole discretion.

                    (v) In the event that any payment or  distribution of assets
of the Company of any kind or character, whether in cash, property or securities
(other than  securities  which are subordinate and junior in right of payment to
the payment in full of all Senior Debt  outstanding  at the time of the issue of
such securities), shall be received by the Holder of this Debenture in violation
of the terms of this Debenture,  such payment or  distribution  shall be held by
the Holder of this  Debenture  in trust for the  benefit  of the  holders of the
Senior Debt and shall,  with or without demand, be immediately paid over (in the
same form in which  received,  with the addition  only of such  endorsements  or
assignments  as may be  necessary)  to the  holders of such Senior Debt or their
representative  or  representatives  or to the  trustee  or  trustees  under any
indenture  under which any  instruments  evidencing  any of such Senior Debt may
have been issued, ratably according to the aggregate amounts remaining unpaid on
account of the Senior Debt held or  represented  by each for  application to the
payment of all Senior Debt  remaining  unpaid  until such Senior Debt shall have
been paid in full, after giving effect to any concurrent payment or distribution
to the holders of such Senior Debt.  The rights  conveyed by this paragraph 3 to
the  holders of the Senior  Debt may be  enforced  by the holders of Senior Debt
directly  against  the Holder of this  Debenture,  the Holder of this  Debenture
acknowledging  that each  holder  of Senior  Debt is an  intended,  third  party
beneficiary of this paragraph 3.

                    (vi) The Holder of this  Debenture  covenants to the holders
of the Senior Debt that the Holder of this Debenture will not take any action or
inaction or permit or direct the taking on its behalf of any action or inaction,
without first having given not less than sixty (60) days prior written notice to
the Company,  to: (A) file any petition against the Company under the Bankruptcy
Code or any insolvency or similar statute, (B) file any petition or complaint to
enforce  the  Debenture,  (C)  file  any  petition  seeking  to have a  receiver
appointed for the Company or any of the Company's assets,  properties or rights,
or (D) file any other petition or action against the Company, unless the holders
of the  Senior  Debt  have  previously  filed a  similar  petition  or action or
consented in writing to the filing thereof.

                    (vii) The Holder of this Debenture  agrees that all payments
received  by the  holders  of the  Senior  Debt  may be  applied,  reversed  and
reapplied,  in whole  or in part,  to any of the  Senior  Debt as the  receiving
holder of the Senior Debt deems  appropriate  without  affecting the validity or
enforceability of the subordination  provisions of this Debenture. The Holder of
this Debenture  hereby  consents to any extension or postponement of the time of
payment of all or any part of the Senior  Debt or to any other  indulgence  with
respect thereto,  and to any substitution,  exchange or release of all or any of
the  collateral or other  security with respect to all or any part of the Senior
Debt,  and to the addition or release of any other party or person  primarily or
secondarily liable therefor.  The holder of any Senior Debt may at any time, and
from time to time,  enter into such agreement or agreements  with the Company as
such holder of Senior Debt may deem proper,  altering the terms of all or any of
the Senior Debt owing to it or affecting the  collateral or other  security with
respect  to such  Senior  Debt or any  guarantee  underlying  any or all of such
Senior Debt, and may exchange,  sell, release,  surrender or otherwise deal with
any such  security  or  guarantees,  without  in any way  thereby  impairing  or
affecting the  provisions  of this  Debenture or the rights and interests of the
holder of the Senior Debt arising hereunder or provided for herein.

                    (viii) The Holder of this  Debenture  hereby agrees that the
holders  of the  Senior  Debt  shall  have no duty to advise  the Holder of this
Debenture  of  information  known  to any of them  regarding  any  condition  or
circumstance,  including  those  described in clause (vii) of this  subparagraph
(b).  The Holder of this  Debenture  acknowledges  and  agrees  that none of the
holders of the Senior  Debt have made any  warranties  or  representations  with
respect  to  the  legality,  validity,   completeness,   enforceability  or  the
collectability of all or any part of the Senior Debt owing to them, and that the
holders of the Senior Debt shall be entitled to manage and  supervise the Senior
Debt in  accordance  with  applicable  law and their  usual  practices,  without
affecting the validity or enforceability of the subordination provisions of this
Debenture.

                    (ix) This is a continuing agreement of subordination and the
holders of the Senior Debt may continue,  at any time and without  notice to the
Holder of this Debenture, to extend credit or other financial accommodations and
loan  monies to or for the  benefit  of the  Company  on the faith  hereof.  The
provisions  in this  paragraph 3 are  unconditional  and  irrevocable  and shall
continue in full force and effect until, with respect to all collateral or other
security interests pledged as security  therefor,  all Senior Debt shall be paid
in full and no further Senior Debt can arise.

                    (x) The  subordination  provisions in this Debenture may not
be changed, waived,  discharged or terminated except by an instrument in writing
signed by the Company  and the holder or holders of Senior Debt whose  rights or
interests  under such Senior  Debt or with  respect to any  collateral  or other
security therefor would be affected thereby,  and then any such change,  waiver,
discharge or  termination  shall be effective  only in respect to the holders of
Senior Debt consenting thereto.

                    (xi) The  subordinations  contained in this Agreement  shall
continue in all events, including, but not limited to, the dissolution,  winding
up,  liquidation  (total  or  partial),  reorganization  (whether  voluntary  or
involuntary) of the Company or the filing of a bankruptcy petition by or against
the Company, or the insolvency of the Company, the appointment of a receiver, or
the  institution  of any other  proceedings  by or against the  Company,  or the
seeking by any creditor in the future to rescind,  amend,  terminate, or reform,
by litigation or otherwise, its respective agreements with the Company.

                    (xii) No  present or future  holder of Senior  Debt shall be
prejudiced in any right to enforce  subordination of the Debenture by any act or
failure to act on the part of the  Company or the Holder of this  Debenture.  No
waiver  shall be  deemed to be made by any  holder of Senior  Debt of any of its
rights  hereunder,  unless the same shall be in writing signed by such holder of
Senior Debt, and each waiver, if any, shall be a waiver only with respect to the
specific  instance  involved  and  shall  in no way  impair  the  rights  or the
obligations of any party to each other in any other respect at any other time.

                    (xiii) The  Holder of this  Debenture,  within a  reasonable
time after  receipt of a request  from the Company or any holder of Senior Debt,
will  prepare,  execute,  obtain  and/or  file all  documents  and take all such
actions which the Company or holder of Senior Debt deems reasonably necessary to
effectuate the lien, priorities and subordinations set forth herein.

               (c) From and after the payment in full of all Senior Debt, to the
extent that the Holder of this  Debenture  is required to turn over funds to any
holder of Senior Debt which were otherwise  properly paid on the Debenture,  the
Holder of this  Debenture  shall be  subrogated  (equally  and ratably  with the
holders of all other  subordinated  debt of the Company of equal ranking) to the
rights of the holders of Senior Debt to receive  payments  or  distributions  of
assets or  securities of the Company  applicable  to the Senior Debt  including,
without limitation,  any assets securing Senior Debt until the Debenture is paid
in  full,  and,  for  purposes  of  such   subrogation,   no  such  payments  or
distributions  to the  holders  of Senior  Debt of assets or  securities,  which
otherwise would have been payable or  distributable to Holder of this Debenture,
shall,  as between the Company,  its creditors  other than the holders of Senior
Debt, and the Holder of this Debenture, be deemed to be a payment by the Company
to or on  account  of the  Debenture,  it being  understood  that the  foregoing
provisions of this  paragraph 3 are intended  solely for the purpose of defining
the relative  rights of the Holder of this  Debenture,  on the one hand, and the
holders of the Senior  Debt,  on the other hand,  and nothing  contained in this
paragraph 3 or elsewhere in this  Debenture is intended to or shall  impair,  as
between the Company, its creditors other than the holders of Senior Debt and the
Holder of this Debenture,  the obligation of the Company, which is unconditional
and absolute, to pay to the Holder of this Debenture the principal, and premium,
if any, and interest on this Debenture as and when the same shall become due and
payable in accordance  with their terms or to affect the relative  rights of the
Holder of this  Debenture and creditors of the Company other than the holders of
the Senior Debt, nor shall anything herein or therein prevent the Holder of this
Debenture  from  exercising all remedies  otherwise  permitted by applicable law
upon default  under the  Debenture,  subject to the rights,  if any,  under this
paragraph  3, of the  holders  of  Senior  Debt to  receive  cash,  property  or
securities otherwise payable or deliverable to the Holder of this Debenture.

               (d) Upon any  distribution  or  payment  in  connection  with any
insolvency  or  bankruptcy  proceedings,   or  any  receivership,   liquidation,
reorganization or other similar proceedings in connection therewith, relative to
the Company, or to its property,  or any proceedings for voluntary  liquidation,
dissolution  or  other  winding  up of the  Company,  whether  or not  involving
insolvency or bankruptcy, the Holder of this Debenture shall be entitled to rely
upon any  order or  decree  of a court of  competent  jurisdiction  in which any
proceedings  are pending or any order or decree of the court  which  entered the
judgment  pursuant to which any such sale was made,  as the case may be, and the
Holder of this  Debenture  shall be entitled to rely upon a  certificate  of the
liquidating  trustee or agent or other person making any distribution or payment
to the Holder of this  Debenture  for the  purpose of  ascertaining  the persons
entitled to  participate  in such  distribution,  the holders of Senior Debt and
other  indebtedness  of the Company,  the amount  thereof or the amount  payable
thereon,  the amount or amounts paid or distributed  thereon and all other facts
pertinent thereto or to this paragraph 3.

               (e) Upon the  request  of the  holders of the  Senior  Debt,  the
Company and the Holder of this Debenture will execute such documents and perform
all such other acts as may be  reasonably  required  to  rescind  any  premature
payment or  performance  of the  Debenture  and to  reestablish,  to the maximum
extent practical, the status quo prior to such premature payment or performance.

         4. Conversion of Debentures.

               (a) At the option of the Holder,  this  Debenture  or any portion
thereof which is $1,000 or an intrical  multiple  thereof may be converted  into
shares of Common Stock.  The conversion price shall equal $1.25 principal amount
of this  Debenture  per share,  subject to  adjustments  as provided  below (the
"Conversion Price"). Such conversion right shall expire at the close of business
on the Business Day immediately preceding the Redemption Date applicable to this
Debenture, if any.

               (b)  To  exercise  the  conversion   privilege  provided  for  in
paragraph  4(a), the Holder of this Debenture  shall surrender this Debenture to
the  Company  together  with the  conversion  notice  in the  form set  forth as
Attachment  A hereto,  duly  executed.  If this  Debenture  is  surrendered  for
conversion  during the period from the close of business on any Interest Payment
Record  Date to the  corresponding  Interest  Payment  Date,  it  shall  also be
accompanied by payment in funds  acceptable to the Company of an amount equal to
the interest  payable on such Interest  Payment Date on the principal  amount of
this  Debenture  then being  converted.  Such  interest  shall be payable to the
Holder notwithstanding such conversion.

               (c) If this  Debenture  is  converted  in part only,  the Company
shall  execute and  deliver to or on the order of the Holder,  at the expense of
the Company,  a new  Debenture or  Debentures  in principal  amount equal to the
portion of this Debenture which is not converted.

               (d) As soon  as  practicable  following  the  conversion  of this
Debenture,  the  Company  will  deliver to the Holder  hereof a  certificate  or
certificates  representing  the number of shares of Common Stock  (excluding any
fractional  shares)  issuable by reason of such conversion in such name or names
in such denomination or denominations as the converting Holder has specified. If
any fractional share of Common Stock would, except for the provisions hereof, be
deliverable  upon  conversion  of  this  Debenture,  the  Company,  in  lieu  of
delivering such factional share, will pay cash in respect thereof based upon the
Conversion Price which would otherwise have been attributable to such fractional
share.  The issuance of certificates  for shares of Common Stock upon conversion
of this  Debenture  will be made  without  charge to the  Holder  hereof for any
issuance  tax in  respect  thereof  or other  cost  incurred  by the  Company in
connection  with such  conversion  and the  related  issuance  of such shares of
Common Stock.

               (e) The  Conversion  Price  is  subject  to  adjustment  upon the
occurrence of any subdivision (by any stock split,  stock dividend or otherwise)
of the  outstanding  shares of Common Stock into a greater number of shares.  In
such case, the Conversion Price in effect  immediately prior to such subdivision
will be proportionately reduced. If the Company at any time combines (by reverse
stock split or otherwise) its outstanding  shares of Common Stock into a smaller
number of  shares,  the  Conversion  Price in effect  immediately  prior to such
combination will be proportionately increased.

         5. Debenture Otherwise Payable.

         Except to the extent specifically provided herein, nothing contained in
this Debenture shall prevent at any time, except under the conditions  described
in paragraph 3 or during the pendency of any  proceedings  therein  referred to,
the Company from making payments at any time on this Debenture.

         6. Nonimpairment.

         Nothing  contained in this Debenture is intended to or shall impair, as
between the Company,  the Company's  creditors  other than the Holders of Senior
Debt and the Holders of the Debentures,  the obligation of the Company, which is
absolute and unconditional, to pay to the Holder of this Debenture the principal
of and  interest on this  Debenture,  as and when the same shall  become due and
payable in  accordance  with its terms,  and which  (subject to the rights under
paragraph 3 of the holders of Senior  Debt) is intended to rank equally with all
other general  obligations of the Company, or is intended to or shall affect the
relative  rights of the Holders of the  Debentures  and creditors of the Company
other than the holders of Senior Debt,  nor shall  anything  herein  prevent the
Holder from exercising all remedies  otherwise  permitted by applicable law upon
the occurrence of an Event of Default (as that term is defined in paragraph 16),
subject to the rights, if any, under paragraph 3 of the holders of Senior Debt.

         7.  Representations, Warranties and Covenants.

         The Company  represents  and  warrants to the Holder as of the original
date of the issuance of the Debenture as follows:

               (a) The Company (i) is a corporation duly  incorporated,  validly
existing and in good standing under the laws of the State of Iowa;  (ii) has all
requisite  corporate  power  and  authority  to own or  lease  and  operate  its
properties and assets, and to carry on its business as now conducted,  and (iii)
is duly  qualified  or  licensed  to do  business  and is in good  standing as a
foreign  corporation in all  jurisdictions  in which the ownership or leasing of
its property or in which the conduct of its  business  requires it so to qualify
or be licensed,  except for such  jurisdictions  where,  in the  aggregate,  the
failure to so qualify or be licensed  would not have a material  adverse  effect
upon the Company and its subsidiaries, taken as a whole;

               (b) The Company has all requisite  corporate  power and authority
to execute, deliver and perform all of its obligations under this Debenture;

               (c) The Company  has  reserved a  sufficient  number of shares of
Common Stock for issuance upon  conversion of the Debentures in accordance  with
paragraph  4. The shares of Common Stock so reserved  have been duly  authorized
and, when issued upon  conversion of the Debenture in accordance  with the terms
of paragraph 4, will be validly issued,  fully paid and  nonassessable  and will
not have been issued in violation of any preemptive or similar rights;

               (d) The  Company has taken all  corporate  actions  necessary  to
authorize it to enter into and perform its obligations  under this Debenture and
to consummate the transactions contemplated hereby;

               (e) This  Debenture is a legal,  valid and binding  obligation of
the  Company,  enforceable  in  accordance  with its  terms,  except  that  such
enforcement may be subject to bankruptcy, insolvency, reorganization, moratorium
or other similar laws now or hereafter in effect  relating to creditors'  rights
generally and general principles of equity;

               (f) Neither the execution, delivery or performance by the Company
of this Debenture nor the consummation of the transactions  contemplated  hereby
will  conflict  with,  violate,  constitute  a breach of or a default  (with the
passage of time or otherwise)  under,  result in the imposition of a lien on any
properties  of the  Company or any of its  subsidiaries  or an  acceleration  of
indebtedness  pursuant  to, or, with  respect to clause (ii) below,  require the
consent of any person (other than consents  already  obtained or waived)  under:
(i) the Amended and Restated  Articles of  Incorporation or Amended and Restated
Bylaws of the Company,  (ii) any  material  bond,  debenture,  note or any other
evidence of indebtedness  or any material  indenture,  mortgage,  deed of trust,
stockholder  agreement or any other agreement or instrument to which the Company
or any of its  subsidiaries  is a party or by  which  any of them is bound or to
which any of their  property or assets is subject,  or (iii) any  material  law,
judgment,   decree,  order,  regulation  or  rule  or  order  of  any  court  or
governmental  agency  or  authority  applicable  to  the  Company  or any of its
subsidiaries or any of their  properties or assets other than any such conflicts
with, violations or breaches of, defaults under, and failures to obtain consents
under, such instruments that are not reasonably likely to have, singly or in the
aggregate,  a material adverse effect on the Company and its subsidiaries  taken
as a whole; and

               (g)  No  consent,   approval  or  authorization  of,  or  filing,
registration or qualification with (collectively, a "consent"), any governmental
or regulatory authority or body is required in connection with or as a condition
to the  execution  and  delivery  by  the  Company  of  this  Debenture,  or the
consummation by the Company of the transactions contemplated hereby.

         8. Financial Information.

         The  Company  will  deliver  to the  Holder a copy of each  annual  and
quarterly  report provided by the Company to its shareholders at the time of the
distribution thereof to its shareholders.

         9. Registration, Transfer and Exchange.

         The  Company  shall  cause to be kept at the  principal  office  of the
Company a record in which, subject to such reasonable regulations as the Company
may prescribe and applicable law, the Company shall provide for the registration
of the Debentures and the registration of transfers of the Debentures.

         Upon  surrender  for  registration  of  transfer  of any portion of the
Debenture at the office of the Company,  the Company  shall execute and deliver,
in the  name of the  designated  transferee  or  transferees,  one or  more  new
Debentures of a like aggregate principal amount.

         At the option of the Holder, the Debenture may be exchanged for another
Debenture or Debentures of any  authorized  denominations,  of a like  aggregate
principal  amount,  upon  surrender  of the  Debenture  to be  exchanged at such
office. Whenever any Debenture is so surrendered for exchange, the Company shall
execute and deliver the  Debenture(s)  which the Holder  making the  exchange is
entitled to receive.

         Any Debenture  issued upon any  registration of transfer or exchange of
the Debenture shall be the valid obligation of the Company,  evidencing the same
debt, and entitled to the same benefits as the Debenture  surrendered  upon such
registration of transfer or exchange.

         Upon the presentation or surrender of the Debenture for registration of
transfer or  exchange,  the  Debenture  shall (if so required by the Company) be
duly endorsed,  or be  accompanied  by a written  instrument of transfer in form
satisfactory to the Company,  duly executed by the Holder thereof or attorney of
the Holder duly  authorized in writing,  with the signature of such person being
guaranteed by a bank or other institution acceptable to the Company.

         No service  charge  shall be made for any  registration  of transfer or
exchange of Debenture,  but the Company may require  payment of a sum sufficient
to cover any tax or other governmental  charge that may be imposed in connection
with any registration of transfer or exchange of Debenture.

         10. Mutilated, Destroyed, Lost and Stolen Debenture.

         If (i) a mutilated  Debenture is  surrendered  to the  Company,  or the
Company receives evidence to its satisfaction of the destruction, loss, or theft
of the  Debenture,  and (ii) there is delivered to the Company such  security or
indemnity as may be required by the Company to save the Company harmless,  then,
in the absence of actual  notice to the  Company  that such  Debenture  has been
acquired by a bona fide  purchaser,  the Company shall  execute and deliver,  in
exchange  for,  or in  lieu  of,  such  mutilated,  destroyed,  lost  or  stolen
Debenture, a new Debenture of like tenor and principal amount.

         In case any such  mutilated,  destroyed,  lost or stolen  Debenture has
become or is about to become due and payable, the Company in its discretion may,
instead of issuing a new  Debenture,  pay the  indebtedness  represented by such
Debenture.

         Upon the  issuance  of any new  Debenture  under  this  paragraph,  the
Company may require  the payment of a sum  sufficient  to cover any tax or other
governmental  charge  that may be  imposed  in  relation  thereto  and any other
expenses connected therewith.

         The  provisions  of this  paragraph 10 are exclusive and (to the extent
lawful)  shall  preclude  all other  rights  and  remedies  with  respect to the
replacement or payment of mutilated, destroyed, lost or stolen Debentures.

         11. Deemed Owner.

         Prior to due  presentment  for  registration of transfer or exchange of
any Debenture,  the Company and any agent of the Company may treat the person in
whose name any Debenture is registered on the Debenture register as the owner of
such Debenture for the purpose of receiving payment of principal of and interest
on such  Debenture and for all other  purposes  whatsoever,  whether or not such
Debenture is overdue, and neither the Company nor any agent of the Company shall
be affected by notice to the contrary.

         12. Acts of Holder.

               (a)  Any  request,  demand,  authorization,   direction,  notice,
consent,  waiver or other  action to be given or taken by the  Holder or Holders
may be embodied in and  evidenced by one or more  instruments  of  substantially
similar tenor signed by such  Holder(s) in person or by agent duly  appointed in
writing;  and, except as herein otherwise expressly provided,  such action shall
become  effective  when such  instrument  or  instruments  are  delivered to the
Company.  Such instrument or instruments  (and the action  embodied  therein and
evidenced  thereby)  are  herein  sometimes  referred  to as  the  "Act"  of the
Holder(s) signing such instrument or instruments. Proof of execution of any such
instrument or of a writing appointing any such agent shall be sufficient for any
purpose of this Debenture and conclusive in favor of the Company, if made in the
manner provided in this paragraph 12.

               (b) The fact and date of the  execution by any Holder of any such
instrument or writing may be proved by the  certificate  of any notary public or
other officer  authorized by law to take  acknowledgments  of deeds,  certifying
that  the  person  signing  such  instrument  or  writing  acknowledged  the due
execution  thereof.  Where such  execution is by an officer of a corporation  or
association  or a  member  of a  partnership  or  an  official  of a  public  or
governmental body, on behalf of such corporation,  association,  partnership, or
public or  governmental  body or by a  fiduciary,  such  certificate  shall also
constitute sufficient proof of such person's authority. The fact and date of the
execution by any Holder of any such  instrument or writing,  or the authority of
the person  executing the same, may also be proved in any other manner which the
Company deems  sufficient and in accordance  with such  reasonable  rules as the
Company may determine.

               (c) The  ownership  of this  Debenture  shall  be  proved  by the
Debenture records maintained by the Company.

               (d)  Any  request,  demand,  authorization,   direction,  notice,
consent,  waiver or other  action by the  Holder  shall bind the Holder of every
Debenture  issued  upon the  registration  of  transfer  thereof or in  exchange
therefor or in lieu thereof,  in respect of anything done or suffered to be done
by the Company in reliance  thereon,  whether or not  notation of such action is
made upon the Debenture.

         13. Notices, etc., to the Company.

         Any request,  demand,  authorization,  direction,  notice,  consent, or
waiver  or Act of  Holder  or  other  document  provided  or  permitted  by this
Debenture to be made upon,  given or furnished  to, or filed with the Company by
any Holder shall be  sufficient  for every  purpose  hereunder if in writing and
mailed,  first class postage  prepaid,  to the Company,  317 Savannah Park Road,
Cedar Falls,  Iowa 50613,  or at such other address as shall have been furnished
in writing to the Holder by the Company for this  purpose,  to the  attention of
the Secretary.

         14.  Notices to Holder; Waiver.

         Where this  Debenture  provides  for notice to the Holder,  such notice
shall be sufficiently  given (unless otherwise  expressly provided herein) if in
writing and mailed,  first class postage prepaid,  to the Holder's address as it
appears on the  Debenture  register,  not later than the  latest  date,  and not
earlier than the earliest date, prescribed for the giving of such notice. In any
case where  notice to the Holder is given by mail,  neither  the failure to mail
such notice,  nor any defect in any notice so mailed,  to the  Debenture  Holder
shall affect the sufficiency of notice given to another Debenture Holder.  Where
this  Debenture  provides  for  notice in any  manner,  notice  may be waived in
writing by the person  entitled to receive  notice,  either  before or after the
event,  and the waiver shall be the equivalent of such notice.  Waiver of notice
by the Holder  shall be filed with the  Company,  but such filing shall not be a
condition  precedent to the  validity of any action taken in reliance  upon such
waiver.

         15. Legal Holidays.

         In any case where any action to be taken under this  Debenture is not a
Business Day, then  (notwithstanding  any other provision of this Debenture) the
taking of such action, including the payment of interest or principal,  need not
be made on such date, but may be made on the next  succeeding  Business Day with
the same  force  and  effect  as if made on the  date  provided  herein,  and no
additional  interest  shall  accrue for the period  from the date any payment is
otherwise required hereunder to such Business Day.

         16.  Events of Default.

         Each of the  following  events  shall  constitute  an event of  default
hereunder (an "Event of Default").  Upon the occurrence of any Event of Default,
the Company shall  immediately  notify the Holders in writing of the  occurrence
thereof.

               (a) Default in the payment of any interest upon this Debenture on
an  Interest  Payment  Date,  which  default  continues  for more  than five (5)
Business Days after the occurrence of such Interest Payment Date.

               (b) Default in the payment of the principal of this  Debenture on
the Maturity Date.

               (c) The failure by the Company  duly to observe or perform in any
material  respect any other of the  covenants  or  agreements  specified in this
Debenture to be observed or performed by the Company for a period of ninety (90)
days after the date on which written notice of such failure,  requiring the same
to be remedied, shall have been given to the Company by the Holder hereof.

               (d) The filing of a petition  against  the  Company or any of its
subsidiaries seeking reorganization,  arrangement,  adjustment or composition of
the Company or any of its subsidiaries, or under the Federal Bankruptcy Act, any
insolvency  act or any  other  applicable  federal  or state  law  dealing  with
creditors  rights  generally,  or the  appointment  of a  receiver,  liquidator,
assignee,  trustee,  sequestrator (or other similar  official) of the Company or
any of its subsidiaries or of any substantial part of their property or an order
for the winding up or liquidation  of any of their  affairs,  and the failure to
obtain the dismissal or a stay of such petition for a period of 45 days.

               (e) The institution by the Company or any of its  subsidiaries of
proceedings,  or the consent by any of them to the  institution of bankruptcy or
insolvency proceedings against any such person or the filing by any of them of a
petition  or answer or  consent  seeking  reorganization  or  release  under the
Federal  Bankruptcy Act, any insolvency act or any other  applicable  federal or
state law dealing with creditors rights generally, or the consent by any of them
to the  filing  of  any  such  petition  or to the  appointment  of a  receiver,
liquidator,  assignee, trustee,  sequestrator (or other similar official) of the
Company or any of its  subsidiaries or of any  substantial  part of any of their
property,  or the  making by any of them of an  assignment  for the  benefit  of
creditors,  or the admission by any of them in writing of their inability to pay
their debts  generally as they become due or the taking of  corporate  action by
the Company or any of its subsidiaries in furtherance of any such action.

         17. Acceleration of Maturity; Rescission and Annulment.

         If an Event of  Default  occurs  and is  continuing  as a result of the
occurrence  of any of the events  identified  in paragraph  16(a) through (c) of
this Debenture, the Holder of this Debenture may declare the entire principal of
this  Debenture to be due and payable  immediately,  by notice in writing to the
Company,  and upon any such declaration such principal shall become  immediately
due and payable.  If an Event of Default occurs and is continuing as a result of
the occurrence of any of the events identified in paragraph 16(d) through (e) of
this  Debenture,  all principal  and accrued and unpaid  interest due under this
Debenture shall automatically become immediately due and payable.

         18. Restoration of Rights and Remedies.

         If the Holder has  instituted  any  proceeding  to enforce any right or
remedy  under  this  Debenture  and such  proceeding  has been  discontinued  or
abandoned for any reason,  or has been determined  adversely to the Holder,  the
Company and the Holder shall,  subject to any  determination in such proceeding,
be restored to their former positions hereunder,  and all rights and remedies of
the Holder shall continue as though no such proceeding had been instituted.

         19. Rights and Remedies Cumulative.

         No right or remedy herein  conferred  upon or reserved to the Holder is
intended  to be  exclusive  of any other  right or remedy,  and every  right and
remedy shall,  to the extent  permitted by law, be cumulative and in addition to
every other right and remedy given hereunder or now or hereafter existing at law
or in equity or  otherwise,  but subject in all  instances to the  provisions of
this Debenture. The assertion or employment of any right or remedy hereunder, or
otherwise, shall not prevent the concurrent assertion or employment of any other
appropriate right or remedy.

         20. Delay or Omission Not Waiver.

         No delay or omission of the Holder of this  Debenture  to exercise  any
right or remedy  accruing  upon any Event of Default shall impair any such right
or remedy or constitute a waiver of any such Event of Default or an acquiescence
therein.

         21. Governing Law - Jurisdiction.

         This  Debenture is made under and will be governed by the internal laws
of the State of Iowa,  without  regard to its conflict of laws  principles.  All
parties  hereto  consent to the  jurisdiction  of any state court located within
Iowa or the federal district court for the Northern  district of Iowa, and waive
personal  service of any and all process.  All service of process may be made by
messenger,  by certified or registered mail, return receipt requested,  directed
(i) if to Company,  at the address  determined in accordance  with paragraph 13,
and  (ii)  if to any  Holder,  at the  address  determined  in  accordance  with
paragraph 14. Each party hereto  waives any  objection  which it may have to any
proceeding  commenced  in these courts  based upon  improper  venue or forum non
conveniens.

         22. Severability Clause.

         In case any provision in this  Debenture  shall be invalid,  illegal or
unenforceable,  the  validity,  legality  and  enforceability  of the  remaining
provisions shall not in any way be affected or impaired thereby.

         23. Certain Defined Terms.

         The following defined terms shall have the meanings specified when used
in this instrument:

               Business  Day - any day  except  Saturday,  Sunday  or any  legal
               holiday or any day on which banking  institutions in Cedar Falls,
               Iowa are closed.

               Common  Stock  -  means  the no par  value  common  stock  of the
               Company.

               Company - means Top Air Manufacturing, Inc, an Iowa corporation.

               Event of Default - is defined in paragraph 16 of this Debenture.

               Federal Bankruptcy Act - means 11 U.S.C., Sections 101 et seq.

               Holder - is defined in paragraph 1 of this Debenture.

               Interest  Payment  Dates - is  defined  on the first page of this
               Debenture.

               Interest Payment Record Dates - is defined in paragraph 1 of this
               Debenture.

               Maturity  Date  - is  defined  in the  first  paragraph  of  this
               Debenture.

               Optional  Redemption  - is the  redemption,  at the option of the
               Company,   permitted  and  described  in  the  first   unnumbered
               paragraph of paragraph 2 of this Debenture.

               Person - means any individual,  partnership,  corporation,  joint
               venture, association, trust or other enterprise or any government
               or   political   subdivision   or  any  agency,   department   or
               instrumentality thereof.

               Prime Rate - the rate announced from time to time by Firstar Bank
               as its prime lending rate.

               Redemption Date - is defined in paragraph 2 of this Debenture.

               Redemption  Price - means the  principal,  premium,  if any,  and
               accrued interest  required to be paid under paragraph 2 hereof in
               respect of any Optional Redemption.

               Senior Debt - is defined in paragraph 3 of this Debenture.

               Senior Debt Default - means the occurrence of a default under the
               terms of any instrument  constituting,  evidencing,  governing or
               securing any Senior Debt which,  upon the giving of notice or the
               passage of time or both,  would  permit the holder of such Senior
               Debt to accelerate the maturity thereof.

               Subsidiary - means any  corporation,  partnership or other entity
               in which the Company  holds,  directly or  indirectly,  more than
               fifty percent (50%) of the outstanding  equity  securities having
               general voting power.

         IN WITNESS WHEREOF,  the Company has caused this Debenture to be signed
as of the 25th day of January, 2000.

                                               TOP AIR MANUFACTURING, INC.

ATTEST:                                         By: /s/ Steven R. Lind
                                                    ----------------------------
                                                    Steven R. Lind
                                                    Title: President and CEO
/s/ Steven F. Bahlmann
--------------------------
              SecretaryTHE DEBENTURE  REPRESENTED BY THIS CERTIFICATE HAS NOT BEEN REGISTERED UNDER THE
SECURITIES  ACT OF  1933,  AS  AMENDED  (THE  "SECURITIES  ACT")  OR  ANY  STATE
SECURITIES  LAWS,  AND NEITHER SUCH  DEBENTURES OR ANY INTERESTS  THEREIN MAY BE
OFFERED,  SOLD,  PLEDGED,   ASSIGNED  OR  OTHERWISE  TRANSFERRED  UNLESS  (I)  A
REGISTRATION  STATEMENT WITH RESPECT  THERETO IS EFFECTIVE  UNDER THE SECURITIES
ACT AND ANY APPLICABLE  STATE  SECURITIES  LAWS, OR (II) THE ISSUER  RECEIVES AN
OPINION OF COUNSEL TO THE HOLDER OF SUCH  DEBENTURE,  WHICH  COUNSEL AND OPINION
ARE REASONABLY  SATISFACTORY TO THE ISSUER,  THAT SUCH DEBENTURE MAY BE OFFERED,
SOLD,  PLEDGED,  ASSIGNED OR TRANSFERRED IN THE MANNER  CONTEMPLATED  WITHOUT AN
EFFECTIVE  REGISTRATION  STATEMENT UNDER THE SECURITIES ACT OR APPLICABLE  STATE
SECURITIES LAWS.

Number
R-002                                                                   $212,000

                           TOP AIR MANUFACTURING, INC.

             CONVERTIBLE SUBORDINATED DEBENTURE DUE JANUARY 15, 2005

         TOP AIR  MANUFACTURING,  INC.,  an  Iowa  corporation  (the  "Company")
promises to pay to Wayne W. Whalen, or registered assigns,  the principal sum of
Two  Hundred  Twelve  Thousand  Dollars,  ($212,000)  on January  15,  2005 (the
"Maturity Date"),  and to pay interest on the principal amount of this Debenture
semi-annually on July 15 and January 15 of each year; provided,  however that if
such date is not a Business Day,  then the Interest  Payment Date shall occur on
the first succeeding Business Day (collectively,  the "Interest Payment Dates"),
commencing  on July 15, 2000.  Interest on the unpaid  principal  balance  shall
accrue from the date hereof at a  fluctuating  rate per annum equal at all times
to one percent  (1%) per annum in excess of the Prime Rate,  with each change in
such  fluctuating   interest  rate  to  take  effect   simultaneously  with  the
corresponding change in the Prime Rate.

         This  Debenture  is  one  of  the  Company's  convertible  subordinated
debentures due 2005 (collectively,  the "Debentures") in the aggregate principal
amount of  $500,000  issued by the  Company in a private  placement  transaction
effected on January 25, 2000.  Certain defined terms used in this instrument are
set forth in paragraph 23 of this Debenture.

         Each of the  Debentures,  including this  Debenture,  is subject to the
following  terms:

         1. Payment.

         The  payment  of  interest  on  this  Debenture  shall  be made on each
Interest  Payment  Date to the Holder  hereof as of the close of business on the
first day of the month in which the subject  Interest  Payment  Date occurs (the
"Interest  Payment  Record Date"),  whether or not such Interest  Payment Record
Date  is a  Business  Day.  Payment  of the  principal  of and  interest  on the
Debentures  will be made at the  principal  office of the  Company or such other
place as may be  designated  by the  Company,  in such coin or  currency  of the
United  States of America as at the time of payment is legal  tender for payment
of public and private debts;  provided,  however,  that payment of principal and
interest  may be made,  at the  option of the  Company,  by check  mailed to the
address of the Holder of the Debentures (each a "Holder," and collectively,  the
"Holders")  entitled  thereto at such address as shall  appear on the  Debenture
records  maintained by the Company.  Interest payable will be paid to the Holder
in whose name the  Debentures  are registered as of the close of business on the
Interest  Payment Record Date which  corresponds to the Interest Payment Date in
question.

         2. Redemption.

         This Debenture is not subject to redemption  prior to January 15, 2002.
Thereafter,  the Debentures will be redeemable, at the option of the Company, at
any time in whole and from time to time in part at: (a) 105% of par from January
15, 2002 to January 15,  2003;  (b) 103% of par from January 15, 2003 to January
15, 2004;  and (c) from and after January 15, 2004,  at par, in each case,  plus
accrued interest.

         If less than all of the Debentures are to be redeemed, the Company will
select  Debentures  for such  partial  redemption  pro  rata or by lot,  and the
Company  may select  for  redemption  portions  of the  principal  amount of any
Debentures of a denomination  larger than $1,000.  In the event of redemption of
this Debenture in part only, a new Debenture(s) for the unredeemed portion shall
be issued in the name of the Holder upon the surrender hereof.

         The Company shall give notice of any redemption  permitted  pursuant to
this paragraph 2 by first class mail,  postage prepaid,  mailed not less than 30
nor  more  than 90 days  prior  to the  date  fixed  for  such  redemption  (the
"Redemption Date"), to each Holder of Debentures to be redeemed,  at the address
of such Holder  appearing in the Debenture  register and otherwise in the manner
prescribed in paragraph 14 hereof.  All such notices of  redemption  shall state
(i) the Redemption  Date, (ii) the Redemption  Price,  (iii) if less than all of
the  Debentures  are to be redeemed,  the  identification  (and,  in the case of
partial  redemption,  the principal  amount) of the particular  Debentures to be
redeemed,  (iv) that on the Redemption Date the Redemption Price will become due
and payable upon each such Debenture,  and that interest  thereon shall cease to
accrue on or after said date, and (v) the place or places where such  Debentures
are to be surrendered for payment of the Redemption Price.

         3. Subordination.

               (a) The indebtedness evidenced by this Debenture and other rights
of the Holder of this  Debenture  granted by or  arising  out of this  Debenture
shall be  unconditionally  subordinated  and  junior  in  priority  and rank and
subject in right of payment,  to the extent and in the manner  herein set forth,
to the prior payment in full of all Senior Debt (as hereinafter defined), and to
all of the liens,  security  interests  and other  rights of the  holders of the
Senior  Debt,  whether  existing on the date hereof or  hereafter  created.  The
subordination  of  priorities  and  all  other  aspects  of  the   subordination
provisions  contained  in this  paragraph  3 shall apply and be  effective:  (i)
regardless of the time or order of perfection or filing of security interests or
the time or order of  attachment  of security  interests,  (ii)  notwithstanding
anything to the contrary contained in the provisions of the Bankruptcy Code, the
Uniform  Commercial  Code in any relevant  statute of the United States,  or the
laws of the  State of Iowa or any  other  relevant  state  which  relate  to the
priority of liens,  security interests or mortgages,  and (iii)  notwithstanding
the lapse of perfection  of liens or security  interests of any holder of Senior
Debt or the  failure  of any  holder  of  Senior  Debt to  perfect  its liens or
security  interests.  "Senior Debt" shall mean the principal of (and premium, if
any), interest accrued or to be accrued, absolute or contingent obligations, and
obligations  acquired  by  purchase  or  otherwise,  as well  as all  reasonable
collection  costs and  attorneys'  fees  incurred  in  enforcing  any rights and
obligations, and all other obligations, liabilities or rights (and, in addition,
of the Company as a debtor-in-possession under any bankruptcy act or code, state
or federal law, common law or equitable doctrine,  and of any trustee,  receiver
or other  party  appointed  for the  Company  under  any such law,  doctrine  or
proceeding):  (A) under any indebtedness of the Company,  whether outstanding on
the date hereof or hereafter  created,  for money borrowed by or loaned to or on
behalf of the Company,  whether or not secured and whether or not the Company is
the  sole  or a  joint  obligor  thereof,  including  but not  limited  to,  any
obligation of the Company to any financial institution under any loan agreement,
instrument,  or letter of credit that has been or will be issued for the account
of the Company;  (B) under any obligations of the Company under any guarantee of
the Company,  whether existing on the date hereof or hereafter  created,  of any
payment  obligation  for money  borrowed by or loaned to any  Subsidiary  of the
Company, whether or not secured; (C) under any deferrals, renewals or extensions
of  any  such  indebtedness  or any  debentures,  notes  or  other  evidence  of
indebtedness  issued in exchange for such Senior  Debt;  and (D) with respect to
any costs, whether payable by way of enforcement or otherwise, which the holders
of the Senior Debt are entitled to be paid or recover.

               (b) (i) Subject to the provisions of clauses (ii), (iii) and (iv)
of this paragraph 3(b), the Company shall make all regularly  scheduled payments
on the Debentures  and all other payments in respect of any Optional  Redemption
of the Debentures  (including  premiums  thereon,  if any), so long as no Senior
Debt Default has occurred or would occur as a result of such payment.

                    (ii) In the  event of any  Senior  Debt  Default,  no amount
shall be paid by the Company in respect to any interest hereon, principal hereof
(whether at maturity by Optional  Redemption  or otherwise) or any other payment
obligation hereunder,  and the Holder of this Debenture shall not be entitled to
receive any amount,  in respect of this  Debenture  unless and until such Senior
Debt  Default  shall have been cured or waived or shall have ceased to exist and
any  acceleration  of Senior Debt  occurring as a result thereof shall have been
rescinded or annulled,  or the Senior Debt to which such default  relates  shall
have been paid in full.

                    (iii) In the event that any Senior Debt is declared  due and
payable  before its  maturity  date because of the  occurrence  of a Senior Debt
Default not cured within any applicable cure periods, the holders of such Senior
Debt shall be entitled to receive payment in full of such Senior Debt before the
Holder of this  Debenture  is  entitled to receive any payment on account of the
Debenture.

                    (iv) In the event of the  liquidation  of the Company or the
distribution  of any of its assets or the securities of any successor on account
of any liquidation, bankruptcy, receivership, reorganization, assignment for the
benefit of creditors or similar  proceeding,  the Holder of this Debenture shall
not be entitled to any payment or distribution on account of the Debenture until
all Senior Debt has been  satisfied  in full,  and the Holder of this  Debenture
shall receive any money,  securities or other  property  distributed in any such
proceeding  on account of the  Debenture in trust for the benefit of the holders
of the Senior  Debt and shall  deliver  any such  property to the holders of the
Senior  Debt in the same form as  received,  adding  only such  endorsements  or
assignments  as may be necessary,  for  application to the  satisfaction  of the
Senior Debt in such order as the holders of the Senior Debt in their  discretion
may determine.  Any excess of such property  remaining after satisfaction of all
of the  Senior  Debt  shall be  returned  to the  Holder  of this  Debenture  or
delivered  as  otherwise  ordered  by any court  having  jurisdiction  over such
proceedings.  The holders of the Senior Debt may liquidate any noncash  property
received from the Holder of this Debenture in the manner in which collateral may
be liquidated  under the terms of the Uniform  Commercial Code as enacted in the
State of Iowa and such  property may be liquidated in any order that the holders
of the Senior Debt shall determine in the exercise of their sole discretion.

                    (v) In the event that any payment or  distribution of assets
of the Company of any kind or character, whether in cash, property or securities
(other than  securities  which are subordinate and junior in right of payment to
the payment in full of all Senior Debt  outstanding  at the time of the issue of
such securities), shall be received by the Holder of this Debenture in violation
of the terms of this Debenture,  such payment or  distribution  shall be held by
the Holder of this  Debenture  in trust for the  benefit  of the  holders of the
Senior Debt and shall,  with or without demand, be immediately paid over (in the
same form in which  received,  with the addition  only of such  endorsements  or
assignments  as may be  necessary)  to the  holders of such Senior Debt or their
representative  or  representatives  or to the  trustee  or  trustees  under any
indenture  under which any  instruments  evidencing  any of such Senior Debt may
have been issued, ratably according to the aggregate amounts remaining unpaid on
account of the Senior Debt held or  represented  by each for  application to the
payment of all Senior Debt  remaining  unpaid  until such Senior Debt shall have
been paid in full, after giving effect to any concurrent payment or distribution
to the holders of such Senior Debt.  The rights  conveyed by this paragraph 3 to
the  holders of the Senior  Debt may be  enforced  by the holders of Senior Debt
directly  against  the Holder of this  Debenture,  the Holder of this  Debenture
acknowledging  that each  holder  of Senior  Debt is an  intended,  third  party
beneficiary of this paragraph 3.

                    (vi) The Holder of this  Debenture  covenants to the holders
of the Senior Debt that the Holder of this Debenture will not take any action or
inaction or permit or direct the taking on its behalf of any action or inaction,
without first having given not less than sixty (60) days prior written notice to
the Company,  to: (A) file any petition against the Company under the Bankruptcy
Code or any insolvency or similar statute, (B) file any petition or complaint to
enforce  the  Debenture,  (C)  file  any  petition  seeking  to have a  receiver
appointed for the Company or any of the Company's assets,  properties or rights,
or (D) file any other petition or action against the Company, unless the holders
of the  Senior  Debt  have  previously  filed a  similar  petition  or action or
consented in writing to the filing thereof.

                    (vii) The Holder of this Debenture  agrees that all payments
received  by the  holders  of the  Senior  Debt  may be  applied,  reversed  and
reapplied,  in whole  or in part,  to any of the  Senior  Debt as the  receiving
holder of the Senior Debt deems  appropriate  without  affecting the validity or
enforceability of the subordination  provisions of this Debenture. The Holder of
this Debenture  hereby  consents to any extension or postponement of the time of
payment of all or any part of the Senior  Debt or to any other  indulgence  with
respect thereto,  and to any substitution,  exchange or release of all or any of
the  collateral or other  security with respect to all or any part of the Senior
Debt,  and to the addition or release of any other party or person  primarily or
secondarily liable therefor.  The holder of any Senior Debt may at any time, and
from time to time,  enter into such agreement or agreements  with the Company as
such holder of Senior Debt may deem proper,  altering the terms of all or any of
the Senior Debt owing to it or affecting the  collateral or other  security with
respect  to such  Senior  Debt or any  guarantee  underlying  any or all of such
Senior Debt, and may exchange,  sell, release,  surrender or otherwise deal with
any such  security  or  guarantees,  without  in any way  thereby  impairing  or
affecting the  provisions  of this  Debenture or the rights and interests of the
holder of the Senior Debt arising hereunder or provided for herein.

                    (viii) The Holder of this  Debenture  hereby agrees that the
holders  of the  Senior  Debt  shall  have no duty to advise  the Holder of this
Debenture  of  information  known  to any of them  regarding  any  condition  or
circumstance,  including  those  described in clause (vii) of this  subparagraph
(b).  The Holder of this  Debenture  acknowledges  and  agrees  that none of the
holders of the Senior  Debt have made any  warranties  or  representations  with
respect  to  the  legality,  validity,   completeness,   enforceability  or  the
collectability of all or any part of the Senior Debt owing to them, and that the
holders of the Senior Debt shall be entitled to manage and  supervise the Senior
Debt in  accordance  with  applicable  law and their  usual  practices,  without
affecting the validity or enforceability of the subordination provisions of this
Debenture.

                    (ix) This is a continuing agreement of subordination and the
holders of the Senior Debt may continue,  at any time and without  notice to the
Holder of this Debenture, to extend credit or other financial accommodations and
loan  monies to or for the  benefit  of the  Company  on the faith  hereof.  The
provisions  in this  paragraph 3 are  unconditional  and  irrevocable  and shall
continue in full force and effect until, with respect to all collateral or other
security interests pledged as security  therefor,  all Senior Debt shall be paid
in full and no further Senior Debt can arise.

                    (x) The  subordination  provisions in this Debenture may not
be changed, waived,  discharged or terminated except by an instrument in writing
signed by the Company  and the holder or holders of Senior Debt whose  rights or
interests  under such Senior  Debt or with  respect to any  collateral  or other
security therefor would be affected thereby,  and then any such change,  waiver,
discharge or  termination  shall be effective  only in respect to the holders of
Senior Debt consenting thereto.

                    (xi) The  subordinations  contained in this Agreement  shall
continue in all events, including, but not limited to, the dissolution,  winding
up,  liquidation  (total  or  partial),  reorganization  (whether  voluntary  or
involuntary) of the Company or the filing of a bankruptcy petition by or against
the Company, or the insolvency of the Company, the appointment of a receiver, or
the  institution  of any other  proceedings  by or against the  Company,  or the
seeking by any creditor in the future to rescind,  amend,  terminate, or reform,
by litigation or otherwise, its respective agreements with the Company.

                    (xii) No  present or future  holder of Senior  Debt shall be
prejudiced in any right to enforce  subordination of the Debenture by any act or
failure to act on the part of the  Company or the Holder of this  Debenture.  No
waiver  shall be  deemed to be made by any  holder of Senior  Debt of any of its
rights  hereunder,  unless the same shall be in writing signed by such holder of
Senior Debt, and each waiver, if any, shall be a waiver only with respect to the
specific  instance  involved  and  shall  in no way  impair  the  rights  or the
obligations of any party to each other in any other respect at any other time.

                    (xiii) The  Holder of this  Debenture,  within a  reasonable
time after  receipt of a request  from the Company or any holder of Senior Debt,
will  prepare,  execute,  obtain  and/or  file all  documents  and take all such
actions which the Company or holder of Senior Debt deems reasonably necessary to
effectuate the lien, priorities and subordinations set forth herein.

               (c) From and after the payment in full of all Senior Debt, to the
extent that the Holder of this  Debenture  is required to turn over funds to any
holder of Senior Debt which were otherwise  properly paid on the Debenture,  the
Holder of this  Debenture  shall be  subrogated  (equally  and ratably  with the
holders of all other  subordinated  debt of the Company of equal ranking) to the
rights of the holders of Senior Debt to receive  payments  or  distributions  of
assets or  securities of the Company  applicable  to the Senior Debt  including,
without limitation,  any assets securing Senior Debt until the Debenture is paid
in  full,  and,  for  purposes  of  such   subrogation,   no  such  payments  or
distributions  to the  holders  of Senior  Debt of assets or  securities,  which
otherwise would have been payable or  distributable to Holder of this Debenture,
shall,  as between the Company,  its creditors  other than the holders of Senior
Debt, and the Holder of this Debenture, be deemed to be a payment by the Company
to or on  account  of the  Debenture,  it being  understood  that the  foregoing
provisions of this  paragraph 3 are intended  solely for the purpose of defining
the relative  rights of the Holder of this  Debenture,  on the one hand, and the
holders of the Senior  Debt,  on the other hand,  and nothing  contained in this
paragraph 3 or elsewhere in this  Debenture is intended to or shall  impair,  as
between the Company, its creditors other than the holders of Senior Debt and the
Holder of this Debenture,  the obligation of the Company, which is unconditional
and absolute, to pay to the Holder of this Debenture the principal, and premium,
if any, and interest on this Debenture as and when the same shall become due and
payable in accordance  with their terms or to affect the relative  rights of the
Holder of this  Debenture and creditors of the Company other than the holders of
the Senior Debt, nor shall anything herein or therein prevent the Holder of this
Debenture  from  exercising all remedies  otherwise  permitted by applicable law
upon default  under the  Debenture,  subject to the rights,  if any,  under this
paragraph  3, of the  holders  of  Senior  Debt to  receive  cash,  property  or
securities otherwise payable or deliverable to the Holder of this Debenture.

               (d) Upon any  distribution  or  payment  in  connection  with any
insolvency  or  bankruptcy  proceedings,   or  any  receivership,   liquidation,
reorganization or other similar proceedings in connection therewith, relative to
the Company, or to its property,  or any proceedings for voluntary  liquidation,
dissolution  or  other  winding  up of the  Company,  whether  or not  involving
insolvency or bankruptcy, the Holder of this Debenture shall be entitled to rely
upon any  order or  decree  of a court of  competent  jurisdiction  in which any
proceedings  are pending or any order or decree of the court  which  entered the
judgment  pursuant to which any such sale was made,  as the case may be, and the
Holder of this  Debenture  shall be entitled to rely upon a  certificate  of the
liquidating  trustee or agent or other person making any distribution or payment
to the Holder of this  Debenture  for the  purpose of  ascertaining  the persons
entitled to  participate  in such  distribution,  the holders of Senior Debt and
other  indebtedness  of the Company,  the amount  thereof or the amount  payable
thereon,  the amount or amounts paid or distributed  thereon and all other facts
pertinent thereto or to this paragraph 3.

               (e) Upon the  request  of the  holders of the  Senior  Debt,  the
Company and the Holder of this Debenture will execute such documents and perform
all such other acts as may be  reasonably  required  to  rescind  any  premature
payment or  performance  of the  Debenture  and to  reestablish,  to the maximum
extent practical, the status quo prior to such premature payment or performance.

         4. Conversion of Debentures.

               (a) At the option of the Holder,  this  Debenture  or any portion
thereof which is $1,000 or an intrical  multiple  thereof may be converted  into
shares of Common Stock.  The conversion price shall equal $1.25 principal amount
of this  Debenture  per share,  subject to  adjustments  as provided  below (the
"Conversion Price"). Such conversion right shall expire at the close of business
on the Business Day immediately preceding the Redemption Date applicable to this
Debenture, if any.

               (b)  To  exercise  the  conversion   privilege  provided  for  in
paragraph  4(a), the Holder of this Debenture  shall surrender this Debenture to
the  Company  together  with the  conversion  notice  in the  form set  forth as
Attachment  A hereto,  duly  executed.  If this  Debenture  is  surrendered  for
conversion  during the period from the close of business on any Interest Payment
Record  Date to the  corresponding  Interest  Payment  Date,  it  shall  also be
accompanied by payment in funds  acceptable to the Company of an amount equal to
the interest  payable on such Interest  Payment Date on the principal  amount of
this  Debenture  then being  converted.  Such  interest  shall be payable to the
Holder notwithstanding such conversion.

               (c) If this  Debenture  is  converted  in part only,  the Company
shall  execute and  deliver to or on the order of the Holder,  at the expense of
the Company,  a new  Debenture or  Debentures  in principal  amount equal to the
portion of this Debenture which is not converted.

               (d) As soon  as  practicable  following  the  conversion  of this
Debenture,  the  Company  will  deliver to the Holder  hereof a  certificate  or
certificates  representing  the number of shares of Common Stock  (excluding any
fractional  shares)  issuable by reason of such conversion in such name or names
in such denomination or denominations as the converting Holder has specified. If
any fractional share of Common Stock would, except for the provisions hereof, be
deliverable  upon  conversion  of  this  Debenture,  the  Company,  in  lieu  of
delivering such factional share, will pay cash in respect thereof based upon the
Conversion Price which would otherwise have been attributable to such fractional
share.  The issuance of certificates  for shares of Common Stock upon conversion
of this  Debenture  will be made  without  charge to the  Holder  hereof for any
issuance  tax in  respect  thereof  or other  cost  incurred  by the  Company in
connection  with such  conversion  and the  related  issuance  of such shares of
Common Stock.

               (e) The  Conversion  Price  is  subject  to  adjustment  upon the
occurrence of any subdivision (by any stock split,  stock dividend or otherwise)
of the  outstanding  shares of Common Stock into a greater number of shares.  In
such case, the Conversion Price in effect  immediately prior to such subdivision
will be proportionately reduced. If the Company at any time combines (by reverse
stock split or otherwise) its outstanding  shares of Common Stock into a smaller
number of  shares,  the  Conversion  Price in effect  immediately  prior to such
combination will be proportionately increased.

         5. Debenture Otherwise Payable.

         Except to the extent specifically provided herein, nothing contained in
this Debenture shall prevent at any time, except under the conditions  described
in paragraph 3 or during the pendency of any  proceedings  therein  referred to,
the Company from making payments at any time on this Debenture.

         6. Nonimpairment.

         Nothing  contained in this Debenture is intended to or shall impair, as
between the Company,  the Company's  creditors  other than the Holders of Senior
Debt and the Holders of the Debentures,  the obligation of the Company, which is
absolute and unconditional, to pay to the Holder of this Debenture the principal
of and  interest on this  Debenture,  as and when the same shall  become due and
payable in  accordance  with its terms,  and which  (subject to the rights under
paragraph 3 of the holders of Senior  Debt) is intended to rank equally with all
other general  obligations of the Company, or is intended to or shall affect the
relative  rights of the Holders of the  Debentures  and creditors of the Company
other than the holders of Senior Debt,  nor shall  anything  herein  prevent the
Holder from exercising all remedies  otherwise  permitted by applicable law upon
the occurrence of an Event of Default (as that term is defined in paragraph 16),
subject to the rights, if any, under paragraph 3 of the holders of Senior Debt.

         7.       Representations, Warranties and Covenants.

         The Company  represents  and  warrants to the Holder as of the original
date of the issuance of the Debenture as follows:

               (a) The Company (i) is a corporation duly  incorporated,  validly
existing and in good standing under the laws of the State of Iowa;  (ii) has all
requisite  corporate  power  and  authority  to own or  lease  and  operate  its
properties and assets, and to carry on its business as now conducted,  and (iii)
is duly  qualified  or  licensed  to do  business  and is in good  standing as a
foreign  corporation in all  jurisdictions  in which the ownership or leasing of
its property or in which the conduct of its  business  requires it so to qualify
or be licensed,  except for such  jurisdictions  where,  in the  aggregate,  the
failure to so qualify or be licensed  would not have a material  adverse  effect
upon the Company and its subsidiaries, taken as a whole;

               (b) The Company has all requisite  corporate  power and authority
to execute, deliver and perform all of its obligations under this Debenture;

               (c) The Company  has  reserved a  sufficient  number of shares of
Common Stock for issuance upon  conversion of the Debentures in accordance  with
paragraph  4. The shares of Common Stock so reserved  have been duly  authorized
and, when issued upon  conversion of the Debenture in accordance  with the terms
of paragraph 4, will be validly issued,  fully paid and  nonassessable  and will
not have been issued in violation of any preemptive or similar rights;

               (d) The  Company has taken all  corporate  actions  necessary  to
authorize it to enter into and perform its obligations  under this Debenture and
to consummate the transactions contemplated hereby;

               (e) This  Debenture is a legal,  valid and binding  obligation of
the  Company,  enforceable  in  accordance  with its  terms,  except  that  such
enforcement may be subject to bankruptcy, insolvency, reorganization, moratorium
or other similar laws now or hereafter in effect  relating to creditors'  rights
generally and general principles of equity;

               (f) Neither the execution, delivery or performance by the Company
of this Debenture nor the consummation of the transactions  contemplated  hereby
will  conflict  with,  violate,  constitute  a breach of or a default  (with the
passage of time or otherwise)  under,  result in the imposition of a lien on any
properties  of the  Company or any of its  subsidiaries  or an  acceleration  of
indebtedness  pursuant  to, or, with  respect to clause (ii) below,  require the
consent of any person (other than consents  already  obtained or waived)  under:
(i) the Amended and Restated  Articles of  Incorporation or Amended and Restated
Bylaws of the Company,  (ii) any  material  bond,  debenture,  note or any other
evidence of indebtedness  or any material  indenture,  mortgage,  deed of trust,
stockholder  agreement or any other agreement or instrument to which the Company
or any of its  subsidiaries  is a party or by  which  any of them is bound or to
which any of their  property or assets is subject,  or (iii) any  material  law,
judgment,   decree,  order,  regulation  or  rule  or  order  of  any  court  or
governmental  agency  or  authority  applicable  to  the  Company  or any of its
subsidiaries or any of their  properties or assets other than any such conflicts
with, violations or breaches of, defaults under, and failures to obtain consents
under, such instruments that are not reasonably likely to have, singly or in the
aggregate,  a material adverse effect on the Company and its subsidiaries  taken
as a whole; and

               (g)  No  consent,   approval  or  authorization  of,  or  filing,
registration or qualification with (collectively, a "consent"), any governmental
or regulatory authority or body is required in connection with or as a condition
to the  execution  and  delivery  by  the  Company  of  this  Debenture,  or the
consummation by the Company of the transactions contemplated hereby.

         8. Financial Information.

         The  Company  will  deliver  to the  Holder a copy of each  annual  and
quarterly  report provided by the Company to its shareholders at the time of the
distribution thereof to its shareholders.

         9. Registration, Transfer and Exchange.

         The  Company  shall  cause to be kept at the  principal  office  of the
Company a record in which, subject to such reasonable regulations as the Company
may prescribe and applicable law, the Company shall provide for the registration
of the Debentures and the registration of transfers of the Debentures.

         Upon  surrender  for  registration  of  transfer  of any portion of the
Debenture at the office of the Company,  the Company  shall execute and deliver,
in the  name of the  designated  transferee  or  transferees,  one or  more  new
Debentures of a like aggregate principal amount.

         At the option of the Holder, the Debenture may be exchanged for another
Debenture or Debentures of any  authorized  denominations,  of a like  aggregate
principal  amount,  upon  surrender  of the  Debenture  to be  exchanged at such
office. Whenever any Debenture is so surrendered for exchange, the Company shall
execute and deliver the  Debenture(s)  which the Holder  making the  exchange is
entitled to receive.

         Any Debenture  issued upon any  registration of transfer or exchange of
the Debenture shall be the valid obligation of the Company,  evidencing the same
debt, and entitled to the same benefits as the Debenture  surrendered  upon such
registration of transfer or exchange.

         Upon the presentation or surrender of the Debenture for registration of
transfer or  exchange,  the  Debenture  shall (if so required by the Company) be
duly endorsed,  or be  accompanied  by a written  instrument of transfer in form
satisfactory to the Company,  duly executed by the Holder thereof or attorney of
the Holder duly  authorized in writing,  with the signature of such person being
guaranteed by a bank or other institution acceptable to the Company.

         No service  charge  shall be made for any  registration  of transfer or
exchange of Debenture,  but the Company may require  payment of a sum sufficient
to cover any tax or other governmental  charge that may be imposed in connection
with any registration of transfer or exchange of Debenture.

         10. Mutilated, Destroyed, Lost and Stolen Debenture.

         If (i) a mutilated  Debenture is  surrendered  to the  Company,  or the
Company receives evidence to its satisfaction of the destruction, loss, or theft
of the  Debenture,  and (ii) there is delivered to the Company such  security or
indemnity as may be required by the Company to save the Company harmless,  then,
in the absence of actual  notice to the  Company  that such  Debenture  has been
acquired by a bona fide  purchaser,  the Company shall  execute and deliver,  in
exchange  for,  or in  lieu  of,  such  mutilated,  destroyed,  lost  or  stolen
Debenture, a new Debenture of like tenor and principal amount.

         In case any such  mutilated,  destroyed,  lost or stolen  Debenture has
become or is about to become due and payable, the Company in its discretion may,
instead of issuing a new  Debenture,  pay the  indebtedness  represented by such
Debenture.

         Upon the  issuance  of any new  Debenture  under  this  paragraph,  the
Company may require  the payment of a sum  sufficient  to cover any tax or other
governmental  charge  that may be  imposed  in  relation  thereto  and any other
expenses connected therewith.

         The  provisions  of this  paragraph 10 are exclusive and (to the extent
lawful)  shall  preclude  all other  rights  and  remedies  with  respect to the
replacement or payment of mutilated, destroyed, lost or stolen Debentures.

         11. Deemed Owner.

         Prior to due  presentment  for  registration of transfer or exchange of
any Debenture,  the Company and any agent of the Company may treat the person in
whose name any Debenture is registered on the Debenture register as the owner of
such Debenture for the purpose of receiving payment of principal of and interest
on such  Debenture and for all other  purposes  whatsoever,  whether or not such
Debenture is overdue, and neither the Company nor any agent of the Company shall
be affected by notice to the contrary.

         12. Acts of Holder.

               (a)  Any  request,  demand,  authorization,   direction,  notice,
consent,  waiver or other  action to be given or taken by the  Holder or Holders
may be embodied in and  evidenced by one or more  instruments  of  substantially
similar tenor signed by such  Holder(s) in person or by agent duly  appointed in
writing;  and, except as herein otherwise expressly provided,  such action shall
become  effective  when such  instrument  or  instruments  are  delivered to the
Company.  Such instrument or instruments  (and the action  embodied  therein and
evidenced  thereby)  are  herein  sometimes  referred  to as  the  "Act"  of the
Holder(s) signing such instrument or instruments. Proof of execution of any such
instrument or of a writing appointing any such agent shall be sufficient for any
purpose of this Debenture and conclusive in favor of the Company, if made in the
manner provided in this paragraph 12.

               (b) The fact and date of the  execution by any Holder of any such
instrument or writing may be proved by the  certificate  of any notary public or
other officer  authorized by law to take  acknowledgments  of deeds,  certifying
that  the  person  signing  such  instrument  or  writing  acknowledged  the due
execution  thereof.  Where such  execution is by an officer of a corporation  or
association  or a  member  of a  partnership  or  an  official  of a  public  or
governmental body, on behalf of such corporation,  association,  partnership, or
public or  governmental  body or by a  fiduciary,  such  certificate  shall also
constitute sufficient proof of such person's authority. The fact and date of the
execution by any Holder of any such  instrument or writing,  or the authority of
the person  executing the same, may also be proved in any other manner which the
Company deems  sufficient and in accordance  with such  reasonable  rules as the
Company may determine.

               (c) The  ownership  of this  Debenture  shall  be  proved  by the
Debenture records maintained by the Company.

               (d)  Any  request,  demand,  authorization,   direction,  notice,
consent,  waiver or other  action by the  Holder  shall bind the Holder of every
Debenture  issued  upon the  registration  of  transfer  thereof or in  exchange
therefor or in lieu thereof,  in respect of anything done or suffered to be done
by the Company in reliance  thereon,  whether or not  notation of such action is
made upon the Debenture.

         13. Notices, etc., to the Company.

         Any request,  demand,  authorization,  direction,  notice,  consent, or
waiver  or Act of  Holder  or  other  document  provided  or  permitted  by this
Debenture to be made upon,  given or furnished  to, or filed with the Company by
any Holder shall be  sufficient  for every  purpose  hereunder if in writing and
mailed,  first class postage  prepaid,  to the Company,  317 Savannah Park Road,
Cedar Falls,  Iowa 50613,  or at such other address as shall have been furnished
in writing to the Holder by the Company for this  purpose,  to the  attention of
the Secretary.

         14.      Notices to Holder; Waiver.

         Where this  Debenture  provides  for notice to the Holder,  such notice
shall be sufficiently  given (unless otherwise  expressly provided herein) if in
writing and mailed,  first class postage prepaid,  to the Holder's address as it
appears on the  Debenture  register,  not later than the  latest  date,  and not
earlier than the earliest date, prescribed for the giving of such notice. In any
case where  notice to the Holder is given by mail,  neither  the failure to mail
such notice,  nor any defect in any notice so mailed,  to the  Debenture  Holder
shall affect the sufficiency of notice given to another Debenture Holder.  Where
this  Debenture  provides  for  notice in any  manner,  notice  may be waived in
writing by the person  entitled to receive  notice,  either  before or after the
event,  and the waiver shall be the equivalent of such notice.  Waiver of notice
by the Holder  shall be filed with the  Company,  but such filing shall not be a
condition  precedent to the  validity of any action taken in reliance  upon such
waiver.

         15. Legal Holidays.

         In any case where any action to be taken under this  Debenture is not a
Business Day, then  (notwithstanding  any other provision of this Debenture) the
taking of such action, including the payment of interest or principal,  need not
be made on such date, but may be made on the next  succeeding  Business Day with
the same  force  and  effect  as if made on the  date  provided  herein,  and no
additional  interest  shall  accrue for the period  from the date any payment is
otherwise required hereunder to such Business Day.

         16.      Events of Default.

         Each of the  following  events  shall  constitute  an event of  default
hereunder (an "Event of Default").  Upon the occurrence of any Event of Default,
the Company shall  immediately  notify the Holders in writing of the  occurrence
thereof.

               (a) Default in the payment of any interest upon this Debenture on
an  Interest  Payment  Date,  which  default  continues  for more  than five (5)
Business Days after the occurrence of such Interest Payment Date.

               (b) Default in the payment of the principal of this  Debenture on
the Maturity Date.

               (c) The failure by the Company  duly to observe or perform in any
material  respect any other of the  covenants  or  agreements  specified in this
Debenture to be observed or performed by the Company for a period of ninety (90)
days after the date on which written notice of such failure,  requiring the same
to be remedied, shall have been given to the Company by the Holder hereof.

               (d) The filing of a petition  against  the  Company or any of its
subsidiaries seeking reorganization,  arrangement,  adjustment or composition of
the Company or any of its subsidiaries, or under the Federal Bankruptcy Act, any
insolvency  act or any  other  applicable  federal  or state  law  dealing  with
creditors  rights  generally,  or the  appointment  of a  receiver,  liquidator,
assignee,  trustee,  sequestrator (or other similar  official) of the Company or
any of its subsidiaries or of any substantial part of their property or an order
for the winding up or liquidation  of any of their  affairs,  and the failure to
obtain the dismissal or a stay of such petition for a period of 45 days.

               (e) The institution by the Company or any of its  subsidiaries of
proceedings,  or the consent by any of them to the  institution of bankruptcy or
insolvency proceedings against any such person or the filing by any of them of a
petition  or answer or  consent  seeking  reorganization  or  release  under the
Federal  Bankruptcy Act, any insolvency act or any other  applicable  federal or
state law dealing with creditors rights generally, or the consent by any of them
to the  filing  of  any  such  petition  or to the  appointment  of a  receiver,
liquidator,  assignee, trustee,  sequestrator (or other similar official) of the
Company or any of its  subsidiaries or of any  substantial  part of any of their
property,  or the  making by any of them of an  assignment  for the  benefit  of
creditors,  or the admission by any of them in writing of their inability to pay
their debts  generally as they become due or the taking of  corporate  action by
the Company or any of its subsidiaries in furtherance of any such action.

         17. Acceleration of Maturity; Rescission and Annulment.

         If an Event of  Default  occurs  and is  continuing  as a result of the
occurrence  of any of the events  identified  in paragraph  16(a) through (c) of
this Debenture, the Holder of this Debenture may declare the entire principal of
this  Debenture to be due and payable  immediately,  by notice in writing to the
Company,  and upon any such declaration such principal shall become  immediately
due and payable.  If an Event of Default occurs and is continuing as a result of
the occurrence of any of the events identified in paragraph 16(d) through (e) of
this  Debenture,  all principal  and accrued and unpaid  interest due under this
Debenture shall automatically become immediately due and payable.

         18. Restoration of Rights and Remedies.

         If the Holder has  instituted  any  proceeding  to enforce any right or
remedy  under  this  Debenture  and such  proceeding  has been  discontinued  or
abandoned for any reason,  or has been determined  adversely to the Holder,  the
Company and the Holder shall,  subject to any  determination in such proceeding,
be restored to their former positions hereunder,  and all rights and remedies of
the Holder shall continue as though no such proceeding had been instituted.

         19. Rights and Remedies Cumulative.

         No right or remedy herein  conferred  upon or reserved to the Holder is
intended  to be  exclusive  of any other  right or remedy,  and every  right and
remedy shall,  to the extent  permitted by law, be cumulative and in addition to
every other right and remedy given hereunder or now or hereafter existing at law
or in equity or  otherwise,  but subject in all  instances to the  provisions of
this Debenture. The assertion or employment of any right or remedy hereunder, or
otherwise, shall not prevent the concurrent assertion or employment of any other
appropriate right or remedy.

         20. Delay or Omission Not Waiver.

         No delay or omission of the Holder of this  Debenture  to exercise  any
right or remedy  accruing  upon any Event of Default shall impair any such right
or remedy or constitute a waiver of any such Event of Default or an acquiescence
therein.

         21. Governing Law - Jurisdiction.

         This  Debenture is made under and will be governed by the internal laws
of the State of Iowa,  without  regard to its conflict of laws  principles.  All
parties  hereto  consent to the  jurisdiction  of any state court located within
Iowa or the federal district court for the Northern  district of Iowa, and waive
personal  service of any and all process.  All service of process may be made by
messenger,  by certified or registered mail, return receipt requested,  directed
(i) if to Company,  at the address  determined in accordance  with paragraph 13,
and  (ii)  if to any  Holder,  at the  address  determined  in  accordance  with
paragraph 14. Each party hereto  waives any  objection  which it may have to any
proceeding  commenced  in these courts  based upon  improper  venue or forum non
conveniens.

         22. Severability Clause.

         In case any provision in this  Debenture  shall be invalid,  illegal or
unenforceable,  the  validity,  legality  and  enforceability  of the  remaining
provisions shall not in any way be affected or impaired thereby.

         23. Certain Defined Terms.

         The following defined terms shall have the meanings specified when used
in this instrument:

               Business  Day - any day  except  Saturday,  Sunday  or any  legal
               holiday or any day on which banking  institutions in Cedar Falls,
               Iowa are closed.

               Common  Stock  -  means  the no par  value  common  stock  of the
               Company.

               Company - means Top Air Manufacturing, Inc, an Iowa corporation.

               Event of Default - is defined in paragraph 16 of this Debenture.

               Federal Bankruptcy Act - means 11 U.S.C., Sections 101 et seq.

               Holder - is defined in paragraph 1 of this Debenture.

               Interest  Payment  Dates - is  defined  on the first page of this
               Debenture.

               Interest Payment Record Dates - is defined in paragraph 1 of this
               Debenture.

               Maturity  Date  - is  defined  in the  first  paragraph  of  this
               Debenture.

               Optional  Redemption  - is the  redemption,  at the option of the
               Company,   permitted  and  described  in  the  first   unnumbered
               paragraph of paragraph 2 of this Debenture.

               Person - means any individual,  partnership,  corporation,  joint
               venture, association, trust or other enterprise or any government
               or   political   subdivision   or  any  agency,   department   or
               instrumentality thereof.

               Prime Rate - the rate announced from time to time by Firstar Bank
               as its prime lending rate.

               Redemption Date - is defined in paragraph 2 of this Debenture.

               Redemption  Price - means the  principal,  premium,  if any,  and
               accrued interest  required to be paid under paragraph 2 hereof in
               respect of any Optional Redemption.

               Senior Debt - is defined in paragraph 3 of this Debenture.

               Senior Debt Default - means the occurrence of a default under the
               terms of any instrument  constituting,  evidencing,  governing or
               securing any Senior Debt which,  upon the giving of notice or the
               passage of time or both,  would  permit the holder of such Senior
               Debt to accelerate the maturity thereof.

               Subsidiary - means any  corporation,  partnership or other entity
               in which the Company  holds,  directly or  indirectly,  more than
               fifty percent (50%) of the outstanding  equity  securities having
               general voting power.

         IN WITNESS WHEREOF,  the Company has caused this Debenture to be signed
as of the 25th day of January, 2000.

                                               TOP AIR MANUFACTURING, INC.

ATTEST:                                         By: /s/ Steven R. Lind
                                                    ----------------------------
                                                    Steven R. Lind
                                                    Title: President and CEO
/s/ Steven F. Bahlmann
--------------------------
              Secretary

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