Document:

<PAGE>

                               EXHIBIT 10.11

                            WORONOCO SAVINGS BANK
                          CHANGE IN CONTROL AGREEMENT

     This AGREEMENT is made effective as of March 19, 1999, by and among
Woronoco Savings Bank (the "Institution" or the "Bank"), a
Massachusetts-chartered savings bank, with its principal administrative office
at 31 Court Street, Westfield, Massachusetts, 01086-0978, Robert W. Thomas
("Executive"), and Woronoco Bancorp, Inc. (the "Holding Company"), a
corporation organized under the laws of the State of Delaware which is the
holding company of the Institution.

     WHEREAS, the Institution recognizes the substantial contribution Executive
has made to the Institution and wishes to protect Executive's position
therewith for the period provided in this Agreement, and

WHEREAS, Executive has agreed to serve in the employ of the Institution.

     NOW, THEREFORE, in consideration of the contribution and responsibilities
of Executive, and upon the other terms and conditions hereinafter provided, the
parties hereto agree as follows:

1.   TERM OF AGREEMENT.
     -----------------

     The term of this Change in Control Agreement (the "Agreement") shall be
deemed to have commenced as of the date first above written and shall continue
for a period of thirty-six (36) full calendar months thereafter.  Commencing on
the first anniversary date of this Agreement and continuing at each anniversary
date thereafter, the Board of Directors of the Institution ("Board") may extend
the Agreement for an additional year.  The Board will review the Agreement and
Executive's performance annually for purposes of determining whether to extend
the Agreement, and the results thereof shall be included in the minutes of the
Board's meeting.

2.   CHANGE IN CONTROL.
     -----------------

     (a) Upon the occurrence of a Change in Control of the Institution or the
Holding Company (as herein defined) followed at any time during the term of
this Agreement by the termination of Executive's employment, other than for
Cause, as defined in Section 2(c) hereof, the provisions of Section 3 shall
apply.  Upon the occurrence of a Change in Control, Executive shall have the
right to elect to voluntarily terminate his employment at any time during the
term of this Agreement following any demotion, loss of title, office or
significant authority, reduction in his annual compensation or benefits, or
relocation of his principal place of employment by more than 25 miles from its
location immediately prior to the Change in Control; provided, however, the
Executive may consent in writing to any such demotion, loss, reduction or

<PAGE>

relocation. The effect of any written consent of the Executive under this
Section 2 (a) shall be strictly limited to the terms specified in such written
consent.

     (b) For purposes of this Agreement, a "Change in Control" shall mean an
event of a nature that: (I) would be required to be reported in response to Item
1 (a) of the current report on Form 8-K, as in effect on the date hereof,
pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 (the
"Exchange Act"); or (ii) results in a Change in Control of the Bank or the
Holding Company within the meaning of the Change in Bank Control Act and the
Rules and Regulations promulgated by the Federal Deposit Insurance Corporation
("FDIC") at 12 C.F.R. [sect] 303.4(a) with respect to the Bank and the Board of
Governors of the Federal Reserve System ("FRB") at 12 C.F.R. [sect] 225.41(b)
with respect to the Holding Company, as in effect on the date hereof; or (iii)
results in a transaction requiring prior FRB approval under the Bank Holding
Company Act of 1956 and the regulations promulgated thereunder by the FRB at 12
C.F.R. [sect] 225.11, as in effect on the date hereof except for the Holding
Company's acquisition of the Bank; or (iv) without limitation such a Change in
Control shall be deemed to have occurred at such time as (A) any "person" (as
the term is used in Sections 13(d) and 14(d) of the Exchange Act) is or becomes
the "beneficial owner" (as defined in Rule 13d-3 under the Exchange Act),
directly or indirectly, of securities of the Bank or the Holding Company
representing 20% or more of the Bank's or the Holding Company's outstanding
securities except for any securities of the Bank purchased by the Holding
Company in connection with the conversion of the Bank to the stock form and any
securities purchased by any tax qualified employee benefit plan of the Bank; or
(B) individuals who constitute the Board of Directors on the date hereof (the
"Incumbent Board") cease for any reason to constitute at least a majority
thereof, provided that any person becoming a director subsequent to the date
hereof whose election was approved by a vote of at least three-quarters of the
directors comprising the Incumbent Board, or whose nomination for election by
the Holding Company's stockholders was approved by the same Nominating Committee
serving under an Incumbent Board, shall be, for purposes of this clause (B),
considered as though he were a member of the Incumbent Board; or (C) a plan of
reorganization, merger, consolidation, sale of all or substantially all the
assets of the Bank or the Holding Company or similar transaction occurs in which
the Bank or Holding Company is not the resulting entity; or (D) solicitations of
shareholders of the Holding Company, by someone other than the current
management of the Holding Company, seeking stockholder approval of a plan of
reorganization, merger or consolidation of the Holding Company or Bank or
similar transaction with one or more corporations as a result of which the
outstanding shares of the class of securities then subject to the plan or
transaction are exchanged for or converted into cash or property or securities
not issued by the Bank or the Holding Company shall be distributed; or (E) a
tender offer is made for 20% or more of the voting securities of the Bank or the
Holding Company.

     (c)  Executive shall not receive termination benefits pursuant to Section 3
hereof upon Termination for Cause.  The term "Termination for Cause" shall mean
termination because of Executive's personal dishonesty, willful misconduct, any
breach of fiduciary duty involving personal profit, intentional failure to
perform stated duties, willful violation of any law, rule or regulation (other
than traffic violations or similar offenses) or final cease-and-desist order or
material breach of any provision of this Agreement. Notwithstanding the
foregoing,

<PAGE>

Executive shall not be deemed to have been Terminated for Cause unless and
until there shall have been delivered to him a Notice of Termination which
shall include a copy of a resolution duly adopted by the affirmative vote of
not less than a majority of the members of the Board at a meeting of the Board
called and held for that purpose (after reasonable notice to Executive and an
opportunity for him, together with counsel, to be heard before the Board),
finding that in the good faith opinion of the Board, Executive was guilty of
conduct justifying Termination for Cause and specifying the particulars thereof
in detail. Executive shall not have the right to receive compensation or other
benefits for any period after Termination for Cause.  During the period
beginning on the date of the Notice of Termination for Cause pursuant to
Section 4 hereof through the Date of Termination, stock options granted to
Executive under any stock option plan shall not be exercisable nor shall any
unvested stock awards granted to Executive under any stock benefit plan of the
Institution, the Holding Company or any subsidiary or affiliate thereof vest.
At the Date of Termination, such stock options and such unvested stock awards
shall become null and void and shall not be exercisable by or delivered to
Executive at any time subsequent to such Date of Termination for Cause.

3.   TERMINATION BENEFITS.
     --------------------

     (a)  Upon the occurrence of a Change in Control, followed at any time
during the term of this Agreement by termination of the Executive's employment
due to: (1) Executive's dismissal or (2) Executive's voluntary termination
pursuant to Section 2(a), unless such termination is due to Termination for
Cause, the Institution and the Holding Company shall pay Executive, or in the
event of his subsequent death, his beneficiary or beneficiaries, or his estate,
as the case may be, a sum equal to three (3) times Executive's "Average Annual
Compensation" (as defined herein) for the five most recent taxable years that
Executive has been employed by the Institution or such lesser number of years
in the event that Executive shall have been employed by the Institution for
less than five years, such "Average Annual Compensation" shall include all
taxable income paid by the Bank, including but not limited to any base salary,
bonuses, and commissions paid or to be paid to Executive, as well as
contributions on Executive's behalf to any pension and/or profit sharing plan,
severance payments, retirement payments, directors or committee fees and fringe
benefits paid or to be paid to the Executive in any such year. At the election
of Executive, which election is to be made prior to a Change in Control, such
payment shall be made in a lump sum. In the event that no election is made,
payment to Executive will be made on a monthly basis in approximately equal
installments during the remaining term of this Agreement.

     (b)  Upon the occurrence of a Change in Control of the Institution or the
Holding Company followed at any time during the term of this Agreement by
Executive's voluntary or involuntary termination of employment, other than for
Termination for Cause, the Institution shall cause to be continued life,
medical and disability coverage substantially identical to the coverage
maintained by the Institution or Holding Company for Executive prior to his
severance, except to the extent such coverage may be changed in its application
to all Institution or Holding Company employees on a nondiscriminatory basis.
Such coverage and payments shall cease upon the expiration of thirty-six (36)
full calendar months from the Date of Termination.

<PAGE>

     (c)  Notwithstanding the preceding paragraphs of this Section 3, in no
event shall the aggregate payments or benefits to be made or afforded to
Executive under said paragraphs (the "Termination Benefits") constitute an
"excess parachute payment" under Section 280G of the Internal Revenue Code of
1986, as amended, or any successor thereto, and in order to avoid such a result
Termination Benefits will be reduced, if necessary, to an amount (the
"Non-Triggering Amount"), the value of which is one dollar ($1.00) less than an
amount equal to three (3) times Executive's "base amount," as determined in
accordance with said Section 280G. The allocation of the reduction required
hereby among the Termination Benefits provided by the preceding paragraphs of
this Section 3 shall be determined by Executive.

4.   NOTICE OF TERMINATION.
     ---------------------

     (a)  Any purported termination by the Institution or by Executive in
connection with a Change in Control shall be communicated by Notice of
Termination to the other party hereto.  For purposes of this Agreement, a
"Notice of Termination" shall mean a written notice which shall indicate the
specific termination provision in this Agreement relied upon and shall set
forth in reasonable detail the facts and circumstances claimed to provide a
basis for termination of Executive's employment under the provision so
indicated.

     (b)  "Date of Termination" shall mean the date specified in the Notice of
Termination (which, in the instance of Termination for Cause, shall not be less
than thirty (30) days from the date such Notice of Termination is given).

     (c)  If, within thirty (30) days after any Notice of Termination is given,
the party receiving such Notice of Termination notifies the other party that a
dispute exists concerning the termination, the Date of Termination shall be the
date on which the dispute is finally determined, either by mutual written
agreement of the parties, by a binding arbitration award, or by a final
judgment, order or decree of a court of competent jurisdiction (the time for
appeal therefrom having expired and no appeal having been perfected) and
provided further that the Date of Termination shall be extended by a notice of
dispute only if such notice is given in good faith and the party giving such
notice pursues the resolution of such dispute with reasonable diligence.
Notwithstanding the pendency of any such dispute in connection with a Change in
Control, in the event that the Executive is terminated for reasons other than
Termination for Cause, the Institution will continue to pay Executive his full
compensation in effect when the notice giving rise to the dispute was given
(including, but not limited to his annual salary) and continue him as a
participant in all compensation, benefit and insurance plans in which he was
participating when the notice of dispute was given, until the earlier of: (1 )
the resolution of the dispute in accordance with this Agreement; or (2) the
expiration of the remaining term of this Agreement as determined as of the Date
of Termination.

<PAGE>

5.   SOURCE OF PAYMENTS.
     ------------------

     It is intended by the parties hereto that all payments provided in this
Agreement shall be paid in cash or check from the general funds of the
Institution. Further, the Holding Company guarantees such payment and provision
of all amounts and benefits due hereunder to Executive and, if such amounts and
benefits due from the Institution are not timely paid or provided by the
Institution, such amounts and benefits shall be paid or provided by the Holding
Company.

6.   EFFECT ON PRIOR AGREEMENTS AND EXISTING BENEFIT PLANS.
     -----------------------------------------------------

     This Agreement contains the entire understanding between the parties hereto
and supersedes any prior agreement between the Institution and Executive, except
that this Agreement shall not affect or operate to reduce any benefit or
compensation inuring to Executive of a kind elsewhere provided. No provision of
this Agreement shall be interpreted to mean that Executive is subject to
receiving fewer benefits than those available to him without reference to this
Agreement.

     Nothing in this Agreement shall confer upon Executive the right to
continue in the employ of Institution or shall impose on the Institution any
obligation to employ or retain Executive in its employ for any period.

7.   NO ATTACHMENT.
     -------------

     (a)  Except as required by law, no right to receive payments under this
Agreement shall be subject to anticipation, commutation, alienation, sale,
assignment, encumbrance, charge, pledge, or hypothecation, or to execution,
attachment, levy, or similar process or assignment by operation of law, and any
attempt, voluntary or involuntary, to affect any such action shall be null,
void, and of no effect.

     (b)  This Agreement shall be binding upon, and inure to the benefit of,
Executive, the Institution and their respective successors and assigns.

8.   MODIFICATION AND WAIVER.
     -----------------------

     (a)  This Agreement may not be modified or amended except by an instrument
in writing signed by the parties hereto.

     (b)  No term or condition of this Agreement shall be deemed to have been
waived, nor shall there be any estoppel against the enforcement of any
provision of this Agreement, except by written instrument of the party charged
with such waiver or estoppel. No such written waiver shall be deemed a
continuing waiver unless specifically stated therein, and each such waiver
shall operate only as to the specific term or condition waived and shall not
constitute a waiver of such term or condition for the future or as to any act
other than that specifically waived.

<PAGE>

9.   REOUIRED REGULATORY PROVISIONS.
     ------------------------------

     Any payments made to Executive pursuant to this Agreement, or otherwise,
are subject to and conditioned upon compliance with 12 U.S.C. [sect]1828(k), 12
C.F.R. Part 359 and 12 C.F.R. Section 545.121 and any rules and regulations
promulgated thereunder.

10.  SEVERABILITY.
     ------------

     If, for any reason, any provision of this Agreement, or any part of any
provision, is held invalid, such invalidity shall not affect any other
provision of this Agreement or any part of such provision not held so invalid,
and each such other provision and part thereof shall to the full extent
consistent with law continue in full force and effect.

11.  HEADINGS FOR REFERENCE ONLY.
     ---------------------------

     The headings of sections and paragraphs herein are included solely for
convenience of reference and shall not control the meaning or interpretation of
any of the provisions of this Agreement. In addition, references to the
masculine shall apply equally to the feminine.

12.  GOVERNING LAW.
     -------------

     The validity, interpretation, performance and enforcement of this
Agreement shall be governed by the laws of the Commonwealth of Massachusetts
applicable to contracts entered into and to be performed entirely within the
Commonwealth of Massachusetts.

13.  ARBITRATION.
     -----------

     Any dispute or controversy arising under or in connection with this
Agreement shall be settled exclusively by arbitration, conducted before a panel
of three arbitrators sitting in a location selected by Executive within fifty
(50) miles from the location of the Institution's main office, in accordance
with the rules of the American Arbitration Association then in effect.
Judgment may be entered on the arbitrator's award in any court having
jurisdiction; provided, however, that Executive shall be entitled to seek
specific performance of his right to be paid until the Date of Termination
during the pendency of any dispute or controversy arising under or in
connection with this Agreement.

14.  PAYMENT OF COSTS AND LEGAL FEES.
     -------------------------------

     All reasonable costs and legal fees paid or incurred by Executive pursuant
to any dispute or question of interpretation relating to this Agreement shall
be paid or reimbursed by the Institution (which payments are guaranteed by the
Holding Company pursuant to Section 5 hereof) if Executive is successful on the
merits pursuant to a legal judgment, arbitration or settlement.

<PAGE>

15.  INDEMNIFICATION.
     ---------------

     (a) The Bank shall provide Executive (including his heirs, executors and
administrators) with coverage under a standard directors' and officers'
liability insurance policy at its expense and shall indemnify Executive (and
his heirs, executors and administrators) as permitted under federal law against
all expenses and liabilities reasonably incurred by him in connection with or
arising out of any action, suit or proceeding in which he may be involved by
reason of his having been a director or officer of the Bank (whether or not he
continues to be a director or officer at the time of incurring such expenses or
liabilities), such expenses and liabilities to include, but not be limited to,
judgments, court costs and attorneys' fees and the cost of reasonable
settlements.

     (b) Any payments made to Executive pursuant to this Section are subject to
and conditioned upon compliance with 12 U.S.C. Section 1828(k), 12 C.F.R. Part
359 and 12 C.F.R. Section 545.121 and any rules or regulations promulgated
thereunder.

16.  SUCCESSOR TO THE INSTITUTION.
     ----------------------------

     The Institution shall require any successor or assignee, whether direct or
indirect, by purchase, merger, consolidation or otherwise, to all or
substantially all the business or assets of the Institution, expressly and
unconditionally to assume and agree to perform the Institution's obligations
under this Agreement, in the same manner and to the same extent that the
Institution would be required to perform if no such succession or assignment
had taken place.

<PAGE>

                                   SIGNATURES

     IN WITNESS WHEREOF, Woronoco Savings Bank and Woronoco Bancorp, Inc. have
caused this Agreement to be executed by their duly authorized officers, and
Executive has signed this Agreement, on the 12th day of May, 1999.

ATTEST:                         WORONOCO SAVINGS BANK

/s/ Terry J. Bennett            By: /s/ Cornelius D. Mahoney
-----------------------             ------------------------
Terry J. Bennett                    Cornelius D. Mahoney
Corporate Secretary                 For the Entire Board of Directors

SEAL

ATTEST:                         WORONOCO BANCORP, INC.

/s/ Terry J. Bennett            By: /s/ Cornelius D. Mahoney
------------------------            ------------------------
Terry J Bennett                     Cornelius D. Mahoney
Corporate Secretary                 For the Entire Board of Directors

SEAL

WITNESS:                        EXECUTIVE

/s/ Terry J. Bennett            By: /s/ Robert W. Thomas
------------------------            --------------------
Terry J Bennett                     Robert W. Thomas
Corporate Secretary<PAGE>

                                 PROMISSORY NOTE
                                 ---------------

U.S. $8,200,000.00                                       Dated: October 10, 2001

                   FOR VALUE RECEIVED, the undersigned, Terra Nitrogen, Limited
Partnership, a Delaware limited partnership ("Borrower"), HEREBY PROMISES TO
                                               --------
PAY to the order of Terra Capital, Inc. ("Lender") on October 15, 2008 (the
                                          ------
"Maturity Date") the principal sum of U.S. $8,200,000 (EIGHT MILLION TWO
  -------------
HUNDRED THOUSAND U.S. DOLLARS AND NO CENTS). Capitalized terms used but not
defined herein shall have the meanings assigned to them in the Indenture (as
defined below).

                   1. Subject to the terms and conditions hereof, Lender agrees
to advance to Borrower on the date hereof such sums as Borrower may request
(the "Advances"). Advances shall be made in lawful money of the United States
       --------
of America ("U.S. Dollars" or "U.S.$") and shall be made in same day or
              ------------
immediately available funds. Subject to the terms and conditions hereof,
Borrower may prepay the Advances. Notwithstanding anything to the contrary
contained herein, (i) the Advances shall be made to Borrower on the date hereof
in the amount of U.S. $8,200,000 and (ii) the maximum amount of Advances that
may be outstanding hereunder is U.S. $8,200,000.

                   2. The Advances will bear interest at a rate per annum from
the date hereof equal to the weighted average interest rate of all borrowings
then outstanding under the Credit Facility, to be computed on the basis of a 360
day year of twelve 30 day months. Borrower promises to pay interest on the
unpaid principal amount of Advances from the date hereof until such principal
amount is paid in full on each April 15 and October 15.

                   3. Both principal and interest are payable in lawful money of
the United States of America to Lender in same day funds. The Advances made by
Lender to Borrower pursuant to the terms hereof, and all payments made on
account of principal thereof, shall be recorded by Lender and, prior to any
transfer hereof, endorsed on the grid attached hereto which is part of this
Promissory Note; provided that the failure of Lender to make any such --------
recordation or endorsement shall not affect the obligations of Borrower
hereunder.

                   4. This Promissory Note is secured by (i) a security
agreement (as amended, amended and restated, supplemented or otherwise modified
in accordance with the terms thereof, the "Security Agreement"), in the form
                                           ------------------
annexed hereto as Exhibit A, among Borrower, TNCLP, Lender, Terra Capital and
                  ---------
the Trustee and dated as of the date hereof and (ii) those certain mortgages (as
amended, amended and restated, supplemented or otherwise modified in accordance
with the terms thereof, the "Mortgages"; together with the Security Agreement
                             ---------
and each other security agreement, mortgage, deed of trust, pledge, collateral
as-

<PAGE>

                                      -2-

signment, charge, debenture or other agreement or instrument from time to time
evidencing or creating any security interest or lien in favor of Lender
encumbering any assets of the type described in the definition of Pledged
Collateral (as defined in the Security Agreement), Mort-gaged Property (as
defined in the Mortgages) or Second Lien Collateral (as defined in the Security
Agreement), in each case as amended, amended and restated, supplemented or
otherwise modified in accordance with the terms thereof, the "Security
                                                              --------
Documents") in the form annexed hereto as Exhibit B between Borrower and Terra
---------                                 ---------
Capital and dated as of the date hereof. Reference is made to the Security
Documents as to the nature and extent of the security (the "Collateral") for
                                                            ----------
this Promissory Note, the rights of Lender and Borrower and Terra Capital with
respect to the Collateral and the acceleration of the maturity of this
Promissory Note, all of the terms of which are hereby incorporated herein by
reference.

         5.       This Promissory Note is unconditionally guaranteed by a
guaranty in the form annexed hereto as Exhibit C.
                                       ---------

         6.       Borrower hereby waives presentment, demand, protest and notice
of any kind. No failure to exercise, and no delay in exercising, any rights
hereunder on the part of the holder hereof shall operate as a waiver of such
rights.

         7.       [Intentionally Omitted.]

         8.       In the event (each, an "Event of Default") that (a) an event
                                          ----------------
set forth in Section 6.1 of the Indenture or Section 9.1 of the Credit Facility
shall occur, (b) Borrower shall fail to pay any principal of any Advance
pursuant to this Promissory Note when the same becomes due and payable, (c)
Borrower or any of its Material Subsidiaries (as defined in the Credit Facility)
shall generally not pay its debts as such debts become due, or shall admit in
writing its inability to pay its debts generally, or shall make a general
assignment for the benefit of creditors, or any proceeding shall be instituted
by or against Borrower or any of its Material Subsidiaries seeking to
adjudicate it a bankrupt or insolvent, or seeking liquidation, winding up or
reorganization, under any law relating to bankruptcy, insolvency or
reorganization or relief of debtors, or seeking the entry of an order for
relief or the appointment of a custodian, receiver, trustee, administrative
receiver, liquidator, provisional liquidator, administrator, custodian or other
similar official for it or for any substantial part of its property and, in the
case of any such proceedings instituted against Borrower or any of its Material
Subsidiaries (but not instituted by it), either such proceedings shall remain
undismissed or unstayed for a period of 30 days or any of the actions sought in
such proceedings shall occur, or (d) Borrower or any of its Material
Subsidiaries shall take any corporate action to authorize any of the actions set
forth in the immediately preceding clause (c) then, and in any such event,
Lender may, by notice to Borrower, declare the Advances and this Promissory
Note, all interest thereon and all other amounts payable under this Agreement
and the Security Documents to be forthwith due and payable, whereupon the
Advances and this Promissory Note, all

<PAGE>

such interest and all such amounts shall become and be forthwith due and
payable, without presentment, demand, protest or further notice of any kind,
all of which are hereby expressly waived by Borrower; provided that in the case
                                                      --------
of the occurrence of an Event of Default referred to in Section 6.1 (vii) or
(viii) of the Indenture or Section 9.1(g) of the Credit Facility,(x)the
obligation of Lender to make Advances shall automatically be terminated and (y)
the Advances and this Promissory Note, all such interest and all such amounts
shall automatically become and be due and payable, without presentment, demand,
protest or any notice of any kind, all of which are hereby expressly waived
by Borrower.

                  9.  [Intentionally Omitted.]

                  10. Pursuant to the applicable Security Document (as defined
in the Indenture), the Lender has assigned all of its rights and remedies under
and in respect of this Promissory Note to U.S. Bank National Association, as
Trustee under the Indenture (and its successors and assigns in such capacity)
for the benefit of the Noteholders (as defined therein), and the Borrower hereby
acknowledges and consent to such assignment.

                  11. This Promissory Note shall be governed by, and construed
 in accordance with, the laws of the State of New York, United States, without
 giving effect to principles of conflict of laws thereof.

                  12. This Promissory Note cannot be amended without the consent
 of holders of a majority of the Notes in the manner provided for in the
 Indenture.

                  13. Borrower shall have the right at its option from time to
time to prepay this Promissory Note in whole or in part without premium or
penalty; provided that in no event may Borrower prior to the Maturity Date
         --------
prepay this Promissory Note below the aggregate principal amount of all Advances
outstanding on the date hereof except to the extent that, after giving effect to
such prepayment, the aggregate principal amount of all Fixed Asset Intercompany
Notes then outstanding exceeds the aggregate principal amount of Notes
outstanding; provided,further, that in the event TNCLP becomes a Wholly Owned
             -------- -------
Subsidiary, Borrower shall have the right at its option to prepay this
Promissory Note in whole without premium of penalty without reference to the
preceding proviso.

<PAGE>

                                       -4-

                                            TERRA NITROGEN, LIMITED
                                               PARTNERSHIP

                                            By: TERRA NITROGEN COMPANY,
                                                 L.P., its general partner

                                            By:   /s/ Mark A. Kalafut
                                               -----------------------------
                                                 Name:  Mark A. Kalafut
                                                 Title: Vice President

Acknowledged and Agreed:

TERRA CAPITAL, INC.

By: /s/ Wynn S. Stevenson
   -------------------------
    Name:  Wynn S. Stevenson
    Title: Vice President

           This Promissory Note is payable to the order of U.S. Bank National
Association, as Trustee.

TERRA CAPITAL, INC.

By: /s/ Wynn S. Stevenson
   ------------------------
    Name:  Wynn S. Stevenson
    Title: Vice President

<PAGE>

                                      -5-

                       ADVANCES AND PAYMENTS OF PRINCIPAL
                       ----------------------------------

                                      Amount of       Unpaid
                    Amount of       Principal Paid   Principal     Notation
       Date          Advance          or Prepaid      Balance       Made By
    ------------  -------------  -----------------  ------------  ------------

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