Document:

<PAGE>

                           ECO SOIL SYSTEMS, INC.
                            10740 THORNMINT ROAD
                         SAN DIEGO, CALIFORNIA 92127

                                                   Dated as of December 21, 1999

TO EACH OF THE PURCHASERS LISTED IN
     THE ATTACHED ANNEX 1

                             Amendment No. 4 to
                     Note and Warrant Purchase Agreement
                     -----------------------------------

Ladies and Gentlemen:

                  Reference is made to the Note and Warrant Purchase
Agreement, dated as of August 25, 1998, as amended by letter agreements dated
March 31, 1999, June 30, 1999 and November 12, 1999 (as so amended, the "Note
Agreement"), among Eco Soil Systems, Inc., a Nebraska corporation (the
"Company"), and Albion Alliance Mezzanine Fund, L.P. and Paribas Capital
Funding LLC (collectively, the "Purchasers"). The Purchasers hold 100% of the
Notes outstanding under the Note Agreement. Capitalized terms used herein
without definition have the meanings specified therefor in the Note Agreement.

                  The Company requests the consent of the Purchasers to
certain amendments of the Notes, the Warrants and the Note Agreement, and the
Purchasers are willing to consent to such amendments, on the terms and
subject to the conditions set forth herein.

                  The parties agree as follows:

                  1. AMENDMENTS. 1.1. AMENDMENT OF SECTION 9.1. Section 9.1
of the Note Agreement is hereby amended and restated to read in its entirety
as follows:

                           "9.1. OPTIONAL PREPAYMENTS. The Company may, at its
          option, upon notice as provided in section 9.4, prepay at any time
          all, or from time to time any part (in an amount of at least
          $1,000,000 in the aggregate or an integral multiple of $1,000 in
          excess thereof) of, the Notes at the principal amount so prepaid,
          without premium."

<PAGE>

                  1.2. AMENDMENT OF SECTION 9.3. Section 9.3 of the Note
Agreement is hereby amended and restated to read in its entirety as follows:

                             "9.3.  PREPAYMENT PREMIUM.  Except as may otherwise
         be provided for in sections 9.2 and 11, no premium shall be due and
         payable by the Company upon the prepayment of the Notes."

                  1.3. AMENDMENT OF SECTION 9.8. Section 9.8 of the Note
Agreement is hereby amended and restated to read in its entirety as follows:

                           "9.8. MANDATORY PREPAYMENT UPON SALE OF EQUITY. In
         the event that at any time there shall be Equity Proceeds, the Company
         shall give prompt written notice thereof to each holder of the Notes,
         by facsimile transmission or registered mail (and shall confirm such
         notice by prompt telephonic advice to an investment officer of each
         such holder). The Company shall promptly (but in no event later than
         five days after the Company's receipt thereof) apply such Equity
         Proceeds to the prepayment of the Notes, at the principal amount so
         prepaid, together with interest on such principal amount accrued to
         such date, in accordance with the following:

                           "(a) the first $7,500,000 of any of such Equity
                  Proceeds received by the Company after December 21, 1999 shall
                  be applied by it to the prepayment of the Notes and accrued
                  interest thereon;

                           "(b) the Company may retain the next $2,500,000 of
                  Equity Proceeds it receives; and

                           "(c) the Company shall apply 50% of all Equity
                  Proceeds it receives after the first $10,000,000 to the
                  prepayment of the Notes and accrued interest thereon.

         "In the event that there shall have been a partial prepayment of the
         Notes under this section 9.8, the Company shall promptly give notice to
         the holders of the Notes, accompanied by an Officers' Certificate
         setting forth the principal amount of each of the Notes that was
         prepaid and specifying how each such amount was determined."

                  1.4. AMENDMENT OF SECTION 10.1. Section 10.1 is hereby amended
by adding at the end of the first paragraph thereof the following new sentence:

                                       2
<PAGE>

         "References herein to section 10.2 shall be interpreted to be
         references to section 10.2 as in effect prior to the amendments
         contained in Amendment No. 4."

                  1.5. AMENDMENT OF SECTIONS 10.2(a), (b) AND (c). Section
10.2(a), (b) and (c) of the Note Agreement are hereby amended and restated to
read in their entirety as follows:

                           "10.2. FINANCIAL COVENANTS. (a) LIMITATION ON SENIOR
          SECURED FUNDED DEBT. The Company will not permit the ratio of (i)
          Senior Secured Funded Debt as of each date listed in the table below,
          to (ii) Consolidated EBITDA for the period of four consecutive fiscal
          quarters of the Company ending on such date, to be greater than the
          ratio set forth opposite such date in the table below:

<TABLE>
<CAPTION>
              Quarter End Date                   Ratio
              ----------------                   -----
<S>                                           <C>
              September 30, 1998              3.75 to 1.0
              December 31, 1998               3.00 to 1.0
              March 31, 1999                  3.00 to 1.0
              June 30, 1999                   6.50 to 1.0
              September 30, 1999              3.52 to 1.0
              September 30, 2000              7.10 to 1.0
              December 31, 2000               3.00 to 1.0
              March 31, 2001                  2.50 to 1.0
              and thereafter
</TABLE>

         "No limitations will be applicable to the quarter-end dates December
         31, 1999, March 31, 2000 or June 30, 2000. The limitation applicable to
         the quarter-end date September 30, 1999, is subject to the waiver
         granted by Amendment No. 3.

                           "(b) LIMITATION ON TOTAL FUNDED DEBT. The Company
         will not permit the ratio of (i) total Funded Debt as of each date
         listed in the table below, to (ii) Consolidated EBITDA for the period
         of four consecutive fiscal quarters of the Company ending on such date,
         to be greater than the ratio set forth opposite such date in the table
         below:

<TABLE>
<CAPTION>
              Quarter End Date               Ratio
              ----------------               -----
<S>                                       <C>
              September 30, 1998          7.00 to 1.0
              December 31, 1998           5.00 to 1.0
              March 31, 1999              5.00 to 1.0
              June 30, 1999               10.55 to 1.0
              September 30, 1999          5.30 to 1.0
              September 30, 2000          11.00 to 1.0
              December 31, 2000           5.00 to 1.0
              March 31, 2001              3.50 to 1.0
              and thereafter
</TABLE>

                                       3
<PAGE>

         "No limitations will be applicable to the quarter-end dates December
         31, 1999, March 31, 2000 or June 30, 2000. The limitation applicable to
         the quarter-end date September 30, 1999, is subject to the waiver
         granted by Amendment No. 3.

                           "(c) MINIMUM INTEREST COVERAGE. The Company will not
         permit the ratio of (i) Consolidated EBITDA for the period of four
         consecutive fiscal quarters of the Company ending on each date listed
         in the table below, to (ii) Interest Expense for such period, to be
         less than the ratio set forth opposite such date in the table below:

<TABLE>
<CAPTION>
              Quarter End Date                           Ratio
              ----------------                           -----
<S>                                                    <C>
              September 30, 1998                       1.60 to 1.0
              December 31, 1998                        2.00 to 1.0
              March 31, 1999                           2.50 to 1.0
              June 30, 1999                            1.10 to 1.0
              September 30, 1999                       2.33 to 1.0
              September 30, 2000                       1.25 to 1.0
              December 31, 2000 and thereafter         2.50 to 1.0
</TABLE>

         "No limitations will be applicable to the quarter-end dates December
         31, 1999, March 31, 2000 or June 30, 2000. The limitation applicable to
         the quarter-end date September 30, 1999, is subject to the waiver
         granted by Amendment No. 3."

                  1.6. AMENDMENT OF SECTION 10.2(d). Section 10.2(d) of the Note
Agreement is hereby amended and restated to read in its entirety as follows:

                           "(d) LIMITATION ON CAPITAL EXPENDITURES. The Company
         will not make or commit to make any Capital Expenditure if the amount
         thereof, taken together with all other Capital Expenditures made by the
         Company during the then fiscal year, would exceed (i) $1,000,000 in the
         case of fiscal year 2000 and (ii) $17,500,000 in the case of all fiscal
         years thereafter."

                  1.7. ADDITION OF SECTION 10.2(e). The Note Agreement is hereby
amended by adding new section 10.2(e) immediately following section 10.2(d)
thereof:

                           "(e) MINIMUM EBITDA. The Company shall not permit
         Consolidated EBITDA for each of the quarters ending on the dates set
         forth below to be less than the amount indicated opposite each such
         date:

                                       4
<PAGE>

<TABLE>
<CAPTION>
              Quarter End Date                          Minimum EBITDA
              ----------------                          --------------
<S>                                                <C>
              December 31, 1999                    $        (2,000,000.00)
              March 31, 2000                       $        (2,000,000.00)
              June 30, 2000                        $         2,700,000.00
              September 30, 2000                   $         4,500,000.00
              December 31, 2000                    $         1,000,000.00"
</TABLE>

                  1.8. AMENDMENT OF SECTION 10.5. Section 10.5 of the Note
Agreement is hereby amended and restated to read in its entirety as follows:

                           "10.5. RESTRICTED PAYMENTS. The Company will not, and
         will not permit any Subsidiary to, directly or indirectly declare,
         order, pay, make or set apart any sum or property for any Restricted
         Payment unless, immediately after giving effect to any such proposed
         action:

                                    "(a) no condition or event shall exist which
                  constitutes an Event of Default or Potential Event of Default;
                  and

                                    "(b) the aggregate amount of all sums and
                  property included in all Restricted Payments directly or
                  indirectly declared, ordered, paid, made or set apart by the
                  Company during the period from the Closing Date to and
                  including the date of such proposed action shall not exceed
                  25% (but, in the case of a deficit, 100%) of Consolidated Net
                  Income for such period."

                  1.9. ADDITION OF SECTION 10.18. The Note Agreement is hereby
amended by adding new section 10.18 immediately following section 10.17 thereof:

                           "10.18. ISSUANCE OF CONTINGENT SHARES. If the Company
         shall have failed to prepay the Notes in full, including all accrued
         interest thereon, on or prior to April 3, 2000, the Company shall issue
         a number of shares of Common Stock (the "Contingent Shares") equal to X
         in the following formula (each holder of the Notes to receive its PRO
         RATA share of such number of shares):

                           "X=[the greater of Y and Z] x (P1/P2)

                           "where

                           "Y=1,000,000 (adjusted for splits, combinations and
                               the like to the date of issuance of the
                               Contingent Shares);

                                       5
<PAGE>

                           "Z=5% of the Common Stock on March 31, 2000,
                                calculated on a fully-diluted basis (giving
                                effect to the issuance of all shares of Common
                                Stock issuable upon the conversion, exchange or
                                exercise of all outstanding securities of the
                                Company convertible into or exchangeable or
                                exercisable for shares of Common Stock);

                        "P(1)=the principal amount of the Notes outstanding on
                                March 31, 2000; and

                        "P(2)=the original principal amount of the Notes."

                  1.10. ADDITION OF SECTION 10.19. The Note Agreement is hereby
amended by adding new section 10.19 immediately following new section 10.18:

                           "10.19. SALE OF EQUITY SECURITIES. Without the
         consent of the holders of at least 60% in principal amount of the Notes
         at the time outstanding, the Company will not, and will not permit any
         Subsidiary to, issue or sell any shares of its capital (other than
         pursuant to the exercise of employee stock options and warrants) or
         securities convertible into or exchangeable or exercisable for shares
         of its capital stock, except that any Subsidiary may issue such shares
         or other securities to the Company. At a minimum (but without
         limitation), the holders of the Notes will require that, concurrently
         with the issuance of any such shares or other securities, the Company
         (a) repay the loan outstanding under the Loan and Security Agreement
         between the Company and Coast Business Credit, (b) pay in advance the
         interest payment to become due on the Notes on February 25, 2000, and
         (c) pay the fees and disbursements of the Noteholders' special counsel
         incurred in connection with the transactions contemplated by Amendment
         No. 3 and Amendment No. 4."

                  1.11. ADDITION OF SECTION 10.20. The Note Agreement is hereby
amended by adding new section 10.20 immediately following new section 10.19:

                           "10.20. REGULATED HOLDERS. If any Regulated Holder
         shall advise the Company that the receipt by such Regulated Holder of
         Warrant Shares or Contingent Shares, as the case may be, would cause
         such Regulated Holder to violate any provision of Applicable Law with
         respect to its ownership of securities of the Company, then at the
         option of such Regulated Holder (i) the Company shall cooperate in any
         reasonable efforts by such Regulated Holder to dispose of Warrant
         Shares or Contingent Shares, as the case may be, to an extent and in a
         manner sufficient in the written

                                       6
<PAGE>

         opinion of counsel to such Regulated Holder (which may be internal
         counsel) to prevent such violation; such efforts to include providing
         (and authorizing such Regulated Holder to provide) financial and other
         information concerning the Company to any prospective purchaser of
         such securities (subject to an appropriate confidentiality agreement);
         or (ii) the Company shall use its best efforts (including using its
         best efforts to cause its Certificate to be amended) to create an
         Equivalent Nonvoting Security with respect to such number of Warrant
         Shares or Contingent Shares, as the case may be, as such Regulated
         Holder may specify, and such Regulated Holder shall be entitled to
         receive upon such exercise or exchange, in lieu of such number of
         Warrant Shares or Contingent Shares otherwise receivable by such
         Regulated Holder, the same number of shares or other units of such
         Equivalent Nonvoting Security."

                  1.12. AMENDMENT TO SECTION 11(c). Section 11(c) of the Note
Agreement is hereby amended and restated to read in its entirety as follows:

                           "(c) if the Company shall default in the performance
         of or compliance with any term contained in sections 10.2, 10.5, 10.7,
         10.18 or 10.19."

                  1.13. ADDITIONAL DEFINITIONS. The following defined terms are
hereby added to section 14 of the Note Agreement in the appropriate alphabetical
order:

                           "AMENDMENT NO. 3: Amendment No. 3 to this Agreement,
          dated as of November 12, 1999.

                           "AMENDMENT NO. 4: Amendment No. 4 to this Agreement,
          dated as of December 21, 1999.

                           "AMENDMENT SHARES: the 402,208 shares of Common Stock
          issued by the Company to the Noteholders pursuant to section 3.2 of
          Amendment No. 4.

                           "APPLICABLE LAW: all provisions of laws, statutes,
         ordinances, rules, regulations, permits or certificates of any
         Governmental Authority applicable to any Person or any of its assets or
         property, and all judgments, injunctions, orders and decrees of all
         courts, arbitrators or Governmental Authorities in proceedings or
         actions in which any such Person is a party or by which any of its
         assets or properties are bound.

                           "CERTIFICATE: the Articles of Incorporation of the
          Company, as amended from time to time.

                                       7
<PAGE>

                           "CONTINGENT SHARES: the meaning specified therefor in
          section 10.18.

                           "EQUITY PROCEEDS: as of any date of determination,
         the aggregate amount of the net cash proceeds received by the Company
         or any of its Subsidiaries from the sale of shares of its capital stock
         (other than pursuant to the exercise of employee stock options or
         warrants) or securities convertible into or exchangeable or exercisable
         for shares of its capital stock, during the period from the date of
         Amendment No. 4 to and including the date of determination; PROVIDED,
         however, that the first $5,000,000 of net cash proceeds received by the
         Company from the sale of equity securities in compliance with section
         10.19 shall be excluded from any determination of Equity Proceeds.

                           "EQUIVALENT NONVOTING SECURITY: with respect to any
         security issued or to be issued by any Person, a security of such
         Person that is identical in rights and benefits to such first security,
         except that (a) the equivalent security shall not be entitled to vote
         on any matter on which holders of voting securities of such Person are
         entitled to vote, other than as required by Applicable Law or with
         respect to any amendment or repeal of any provision of the
         Organizational Documents of such Person or any other agreement or
         instrument pursuant to which the equivalent security was issued which
         provision specifically affects such equivalent security, (b) subject to
         such reasonable restrictions as any affected Regulated Holder may
         request (including any restriction necessary to prevent the violation
         by such Regulated Holder of any provision of Applicable Law with
         respect to its ownership of voting securities), the equivalent security
         shall be convertible on a one-to-one ratio into the first security and
         (c) the terms of the equivalent security shall include such provisions
         requested by any affected Regulated Holder as are reasonable and
         equitable to ensure that (i) the equivalent security is treated
         comparably to the first security with respect to dividends,
         distributions, stock or unit splits, reclassifications, capital
         reorganizations, mergers, consolidations and other similar events and
         transactions, (ii) the conversion right provided in clause (b) above is
         equitably protected and (iii) the acquisition of the equivalent
         security will not cause such Regulated Holder to violate Applicable
         Law.

                           "GOVERNMENTAL AUTHORITY: any federal, state,
         municipal or other governmental department, commission, board, bureau,
         agency or instrumentality, or any court, in each case whether of the
         United States of America or foreign.

                                       8
<PAGE>

                           "ORGANIZATIONAL DOCUMENTS: with respect to any
         Person, each instrument or other document that (a) defines the
         existence of such Person, including its articles or certificate of
         incorporation or certificate of formation, as filed or recorded with an
         applicable Governmental Authority or (b) governs the internal affairs
         of such Person, including its bylaws, operating agreement, regulations
         or partnership agreement, in each case as amended, supplemented or
         restated.

                           "OTHER SECURITIES: any stock (other than Common
         Stock) and other securities of the Company or any other Person
         (corporate or otherwise) which the holders of the Warrants at any time
         shall be entitled to receive, or shall have received, upon the exercise
         of the Warrants, in lieu of or in addition to Common Stock, or which at
         any time shall be issuable or shall have been issued in exchange for or
         in replacement of Common Stock or Other Securities pursuant to section
         3 of the Warrants or otherwise.

                           "REGULATED HOLDER: any holder (i) that directly, or
         indirectly because of its ownership by an entity that is subject to
         Regulation Y, is subject to the provisions of Regulation Y and (ii)
         that holds shares of Common Stock or Warrants.

                           "REGULATION Y: Regulation Y of the Board of Governors
          of the Federal Reserve System, 12 C.F.R. Part 225, or any successor
          thereto.

                           "WARRANT SHARES: (a) any shares of Common Stock or
         Other Securities issued or issuable upon exercise of the Warrants and
         (b) any securities issued or issuable with respect to any Common Stock
         or Other Securities referred to in subdivision (a) by way of stock
         dividend or stock split or in connection with a combination of shares,
         recapitalization, merger, consolidation or other reorganization or
         otherwise."

                  1.14. AMENDMENT OF CERTAIN DEFINITIONS. The following defined
terms used in the definition of "Make Whole Premium" are hereby amended and
restated to read in their entirety as follows:

                           "CALLED PRINCIPAL: with respect to any Note, the
          principal of such Note that is declared to be immediately due and
          payable pursuant to section 11.

                           "SETTLEMENT DATE: with respect to the Called
          Principal of any Note, the date on which such Called Principal is
          declared to be immediately due and payable pursuant to section 11."

                                       9
<PAGE>

                  1.15. REFERENCES TO "WARRANTS". From and after the
effectiveness of this Amendment No. 4 and the execution and delivery of the
amended Warrants as contemplated by section 3.1, any reference to the "Warrants"
in the Note Agreement shall be deemed to refer to the Warrants as amended
pursuant to this Amendment No. 4.

                  1.16. AMENDMENT OF SCHEDULES AND EXHIBITS. Each of Schedules
A, C and D and Exhibit B to the Note Agreement is hereby amended and restated to
read in its entirety as set forth in Annexes 1, 2, 3 and 4, respectively,
attached to this Amendment No. 4.

                  2. REPRESENTATIONS AND WARRANTIES. The Company hereby
represents and warrants that:

                  2.1. ORGANIZATION, STANDING, ETC. The Company and each of its
Subsidiaries listed in Annex 2 is a corporation duly organized, validly existing
and in good standing under the laws of the jurisdiction of its incorporation,
and the Company has all requisite corporate power and authority (a) to own and
operate its properties; (b) to carry on its business as now conducted and as
proposed to be conducted; (c) to enter into and carry out the terms of this
Amendment No. 4; (d) to issue the shares issued or to be issued as contemplated
by sections 1.9 and 3.2 of this Amendment No. 4; and (e) to issue, and carry out
the terms of, the Warrants (as amended as contemplated hereby).

                  2.2. CAPITAL STOCK AND RELATED MATTERS. The authorized
capital stock of the Company consists of 50,000,000 shares of Common Stock
and 5,000,000 shares of Preferred Stock, par value $.005. After giving effect
to the transactions contemplated hereby (but excluding the shares to be
issued as contemplated by section 1.9 of this Amendment No. 4), 18,322,963
shares of Common Stock and no shares of Preferred Stock will be issued and
outstanding. All of the outstanding shares of capital stock of the Company
and each of its Subsidiaries are validly issued, fully paid and
non-assessable, and all such shares indicated in Annex 2 as owned by the
Company or by any other Subsidiary are so owned beneficially and of record by
the Company or by such other Subsidiary free and clear of any Lien except
such as are of the character permitted by section 10.3 of the Note Agreement.
The shares of Common Stock issuable upon the exercise of the Warrants, as
amended as contemplated by this Amendment No. 4, have been duly authorized
and validly reserved for issuance upon such exercise and, when so issued,
will be validly issued, fully paid and non-assessable. As of the date hereof,
the Company will not have outstanding securities convertible into or
exchangeable for any shares of its capital stock, nor will it have
outstanding any rights to subscribe for or to purchase, or any options for
the purchase of, or any

                                       10
<PAGE>

agreements providing for the issuance (contingent or otherwise) of, or any
calls, commitments or claims of any character relating to, any shares of its
capital stock or any securities convertible into or exchangeable for any
shares of its capital stack, other than those listed on Annex 3.

                  2.3. NO DEFAULTS. As of the date hereof, no condition or
event exists which constitutes an Event of Default or Potential Event of
Default.

                  3. CONDITIONS TO EFFECTIVENESS. The effectiveness of the
waivers, amendments and other agreements contemplated hereby is subject to the
fulfillment, to the satisfaction of the Purchasers, of the following conditions:

                  3.1. AMENDED WARRANTS. The Company shall have executed and
delivered to each of the Purchasers an amended and restated Warrant,
substantially in the form set out in Annex 4 hereto, for the purchase by the
Purchasers of an aggregate of 662,461 shares of Common Stock, against surrender
by each such Purchaser of the original Warrants for cancellation.

                  3.2. ISSUANCE OF SHARES OF COMMON STOCK. As consideration for
the agreement of the Purchasers to amend certain covenants and to forego
prepayment premiums and the other agreements of the Purchasers contained herein,
the Company shall have issued to each of the Purchasers the number of shares of
Common Stock specified opposite such Purchaser's name in Annex 1 attached hereto
under the heading "Number of Shares of Common Stock", and the Company shall have
delivered to such Purchaser certificates representing such shares.

                  3.3. REGISTRATION RIGHTS AGREEMENT. The Company shall have
executed and delivered to each of the Purchasers the Registration Rights
Agreement, substantially in the form of Annex 5.

                  3.4. NO DEFAULT. The Company shall have delivered to each of
the Purchasers an Officer's Certificate stating that as of the date hereof, and
after giving effect to the transactions contemplated hereby, no Event of Default
or Potential Event of Default has occurred and is continuing.

                  3.5. CONSENTS, AGREEMENTS. The Company shall have obtained
all other consents and waivers necessary in connection with the transactions
contemplated hereby, and such consents and waivers shall be in full force and
effect on the date hereof. A complete and correct copy of each of such
consents and waivers shall have been delivered to the Purchasers.

                                       11
<PAGE>

                  3.6. PROCEEDINGS AND DOCUMENTS. All corporate and other
proceedings in connection with the transactions contemplated by this
Agreement and all documents and instruments incident to such transactions
shall be satisfactory to the Purchasers and their special counsel, and the
Purchasers and their special counsel shall have received all such counterpart
originals or certified or other copies of such documents as it or they may
reasonably request.

                  3.7. OPINION OF COUNSEL. The Purchasers shall have received
from Latham & Watkins, counsel for the Company, and from Fitzgerald, Schorr,
Barmettler & Brennan, P.C., Nebraska counsel for the Company, favorable
opinions substantially in the form set forth in Annex 6-A and 6-B,
respectively, addressed to the Purchasers, dated the effective date of this
Amendment No. 4 and otherwise satisfactory in substance and form to the
Purchasers.

                  4. INTENT OF PURCHASERS. Each Purchaser represents that (A)
it is acquiring the shares of Common Stock and amended Warrants hereunder for
its own account, not with a view to the distribution thereof or with any
present intention of distributing or selling any of such shares or amended
Warrants except in compliance with the Securities Act and any applicable
state securities laws, PROVIDED that the disposition of each Purchaser's
property shall at all times be within its control and (B) it is an
"accredited investor" within the meaning of Rule 502 of the Securities Act.

                  5. RATIFICATION. Except as amended hereby, all of the
provisions of the Note Agreement shall remain in full force and effect.

                  6. MISCELLANEOUS. This Agreement shall be binding upon and
inure to the benefit of and be enforceable by the respective successors and
assigns of the parties hereto, whether so expressed or not. THIS AGREEMENT
SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH AND GOVERNED BY THE LAW OF
THE STATE OF NEW YORK.  The headings in this Agreement are for purposes of

                                       12
<PAGE>

reference only and shall not limit or otherwise affect the meaning hereof. This
Agreement may be executed in any number of counterparts, each of which shall be
an original, but all of which together shall constitute one instrument.

                    [SIGNATURES APPEAR ON THE FOLLOWING PAGE]

                                       13
<PAGE>

                  If the Purchasers are in agreement with the foregoing,
please sign the form of agreement on the accompanying counterparts of this
letter and return one of the same to the Company, whereupon this letter shall
become a binding agreement between the Purchasers and the Company.

                                           Very truly yours,

                                           ECO SOIL SYSTEMS, INC.

                                           By:
                                              --------------------------
The foregoing Amendment is
hereby agreed to as of the
date hereof.

ALBION ALLIANCE MEZZANINE FUND, L.P.

By:  Albion Alliance LLC,
     its General Partner

         By:
            -------------------------
         Name:  Peter C. Gummeson
         Title: Senior Vice President

PARIBAS CAPITAL FUNDING LLC

By:
    -------------------------
Name:  Jeff Youle
Title: Managing Director

                                       14<PAGE>

                             ECO SOIL SYSTEMS, INC.
                              10740 THORNMINT ROAD
                           SAN DIEGO, CALIFORNIA 92127

                                                    Dated as of January 21, 2000

TO EACH OF THE PURCHASERS LISTED IN
     THE ATTACHED ANNEX 1

                               Amendment No. 5 to
                       Note and Warrant Purchase Agreement

                               Amendment No. 1 to
                          Registration Rights Agreement
                          -----------------------------

Ladies and Gentlemen:

                  Reference is made to the Note and Warrant Purchase
Agreement, dated as of August 25, 1998, as amended by letter agreements dated
March 31, 1999, June 30, 1999, November 12, 1999, and December 21, 1999 (as
so amended, the "Note Agreement"), among Eco Soil Systems, Inc., a Nebraska
corporation (the "Company"), and Albion Alliance Mezzanine Fund, L.P. and
Paribas Capital Funding LLC (collectively, the "Purchasers"); and to the
Registration Rights Agreement, dated as of December 21, 1999 (the
"Registration Rights Agreement"), among the Company and each of the
Purchasers. The Purchasers hold 100% of the Notes outstanding under the Note
Agreement. Capitalized terms used herein without definition have the meanings
specified therefor in the Note Agreement.

                  The Company requests the consent of the Purchasers to
certain transactions and to certain amendments of the Note Agreement and the
Registration Rights Agreement, and the Purchasers are willing to consent to
such transactions and amendments, on the terms and subject to the conditions
set forth herein.

                  The parties agree as follows:

                  1. CONSENT TO INCURRENCE OF DEBT. The Purchasers hereby
consent to the incurrence today by the Company of $4,500,000 principal amount
of Debt pursuant to the 7% Debentures. The Purchasers acknowledge and agree
for the benefit of the holder or holders of the 7% Debentures from time to
time that the Debt of the Company outstanding thereunder (notwithstanding any
restriction in the Note Agreement that would have prohibited the incurrence
of such Debt in the absence of

<PAGE>

this consent) is "Superior Debt" for all purposes of section 13 of the Note
Agreement. The Purchasers have reviewed the 7% Debentures, the Convertible
Debentures and Warrants Purchase Agreement pursuant to which the 7%
Debentures are being issued, and the related ancillary documentation, and
such instruments and documents are satisfactory to the Purchasers.

                  2. AMENDMENTS TO THE NOTE AGREEMENT. 2.1. AMENDMENT OF
SECTION 10.19. Section 10.19 of the Note Agreement is hereby amended and
restated to read in its entirety as follows:

                           "10.19. SALE OF EQUITY SECURITIES. Without the
         consent of the holders of at least 60% in principal amount of the Notes
         at the time outstanding, the Company will not, and will not permit any
         Subsidiary to, issue or sell any shares of its capital stock (other
         than pursuant to (i) the exercise of employee stock options and
         warrants and (ii) Earn Out Obligations) or securities convertible into
         or exchangeable or exercisable for shares of its capital stock, except
         that without such consent (a) any Subsidiary may issue such shares or
         other securities to the Company and (b) the Company may sell shares of
         Common Stock at a price of not less than $2.50 per share with warrant
         coverage of up to 40% (I.E., with warrants attached permitting the
         purchase, for an exercise price of not less than $2.50 per share, of a
         number of additional shares not exceeding 40% of the number of shares
         of Common Stock so issued) for aggregate proceeds of up to $3,500,000."

                  2.2. ADDITIONAL DEFINITIONS. The following defined terms are
hereby added to section 14 of the Note Agreement in the appropriate alphabetical
order:

                           "AMENDMENT NO. 5:  Amendment No. 5 to this Agreement,
 dated as of January 21, 2000.

                           "7% DEBENTURES:  the 7% Senior Secured Convertible
         Debentures due January 21, 2001 of the Company, to be issued on January
         21, 2000 in the principal amount of $4,500,000."

                  2.3. AMENDMENT OF CERTAIN DEFINITIONS. The following defined
term is hereby amended and restated to read in its entirety as follows:

                           "EQUITY PROCEEDS: as of any date of determination,
         the aggregate amount of the net cash proceeds received by the Company
         or any of its Subsidiaries from the sale of shares of its capital stock
         (other than pursuant to the exercise of employee stock options or
         warrants) or securities convertible into or exchangeable or exercisable
         for shares of its capital stock, during the period from the

                                       2
<PAGE>

         date of Amendment No. 4 to and including the date of determination;
         PROVIDED that the first $8,000,000 of net cash proceeds received by
         the Company from the sale of equity securities (including the 7%
         Debentures) in compliance with section 10.19 shall be excluded from
         any determination of Equity Proceeds."

                  3. AMENDMENTS TO THE REGISTRATION RIGHTS AGREEMENT. 3.1.
ADDITION OF SECTION 2.8. The Registration Rights Agreement is hereby amended by
adding new section 2.8 immediately following section 2.7 thereof:

                           "2.8. ADDITIONAL HOLDBACK AGREEMENTS. The holders of
         Registrable Securities agree, for the benefit of the holders of the 7%
         Debentures, that they will not effect any public sale or distribution
         of any of the Registrable Securities, except as permitted by the
         following provisions of this section 2.8, until the earlier of (a)
         January 21, 2001 and (b) the date on which there shall no longer exist
         any "7% Debentures Registrable Securities" (as defined in section 1).
         The holders of Registrable Securities may include pursuant to section
         2.1 up to 402,208 shares of Common Stock held by them in any
         registration initiated by the holders of the 7% Debentures, PROVIDED
         that such shares will not be sold or distributed pursuant to such
         registration except in accordance with the following schedule:

                                    "(i) 100,000 of such shares may be sold or
                  distributed at any time after the date such registration is
                  declared effective by the Commission (the "Effective Date");

                                    "(ii) an additional 100,000 of such shares
                  may be sold or distributed at any time after the day that is
                  ninety days after the Effective Date;

                                    "(iii) an additional 100,000 of such shares
                  may be sold or distributed at any time after the day that is
                  one hundred eighty days after the Effective Date; and

                                    "(iv) all of such shares may be sold or
                  distributed at any time after the day that is two hundred
                  seventy days after the Effective Date.

"Each holder of Registrable Securities hereunder may sell or distribute up to
its PRO RATA share of each aggregate amount permitted by the foregoing clauses
to be sold or distributed."

                                       3
<PAGE>

                  3.2. ADDITIONAL DEFINITION. The following defined terms are
hereby added to section 1 of the Registration Rights Agreement in the
appropriate alphabetical order:

                           "AMENDMENT NO. 5: Amendment No. 5 to the Note
          Agreement, dated as of January 21, 2000, among the Company and the
          Investors.

                           "7% DEBENTURES REGISTRABLE SECURITIES: "Registrable
          Securities" as defined in the registration rights agreement pursuant
          to which the holders of the 7% Debentures have registration rights."

                  3.2. AMENDMENT OF DEFINITION. The following defined term is
hereby amended and restated to read in its entirety as follows:

                           "AMENDMENT SHARES: the 402,208 Shares and the 200,000
          Shares issued pursuant to section 4.2 of Amendment No. 4 and section
          5.1 of Amendment No. 5, respectively, to the Investors on a pro rata
          basis."

                  4. REPRESENTATIONS AND WARRANTIES. The Company hereby
represents and warrants that:

                  4.1. ORGANIZATION, STANDING, ETC. Each of the Company and
its Subsidiaries is a corporation duly organized, validly existing and in
good standing under the laws of the jurisdiction of its incorporation and has
all requisite corporate power and authority to own and operate its properties
and to carry on its business as now conducted and as proposed to be
conducted; and the Company has all requisite power and authority to enter
into and carry out the terms of this Amendment No. 5 and the transactions
contemplated by this Amendment No. 5.

                  4.2. NO DEFAULTS. As of the date hereof, no condition or
event exists which constitutes an Event of Default or Potential Event of
Default.

                  5. CONDITIONS TO EFFECTIVENESS. The effectiveness of the
waivers, amendments and other agreements contemplated hereby is subject to
the fulfillment, to the satisfaction of the Purchasers, of the following
conditions:

                  5.1. ISSUANCE OF SHARES OF COMMON STOCK. As consideration
for the agreement of the Purchasers to consent to the incurrence of Debt
under the 7% Debentures and the other agreements of the Purchasers contained
herein, the Company shall have issued to each of the Purchasers the number of
shares of Common Stock specified opposite such Purchaser's name in Annex 1

                                       4
<PAGE>

attached hereto under the heading "Number of Shares of Common Stock to be
Issued in Connection with Amendment No. 5", and the Company shall have
delivered to such Purchaser certificates representing such shares.

                  5.2. CONSENTS, AGREEMENTS. The Company shall have obtained
all consents and waivers necessary in connection with the transactions
contemplated hereby, and such consents and waivers shall be in full force and
effect on the date hereof.

                  5.3. PROCEEDINGS AND DOCUMENTS. All corporate and other
proceedings in connection with the transactions contemplated by this
Amendment No. 5 and all documents and instruments incident to such
transactions shall be satisfactory to the Purchasers and their special
counsel, and the Purchasers and their special counsel shall have received all
such counterpart originals or certified or other copies of such documents as
it or they may reasonably request.

                  5.4. PAYMENT OF INTEREST. The Company shall have paid in
advance the interest payment to become due on the Notes on February 25, 2000.

                  5.5. LEGAL FEES. The Company shall have paid the fees and
disbursements of the Purchasers' special counsel incurred in connection with
the transactions contemplated by Amendments Nos. 3, 4 and 5 and set forth in
a statement delivered to the Company on or prior to the date hereof.

                  6. INTENT OF PURCHASERS. Each Purchaser represents that (a)
it is acquiring the shares of Common Stock hereunder for its own account, not
with a view to the distribution thereof or with any present intention of
distributing or selling any of such shares except in compliance with the
Securities Act and any applicable state securities laws, PROVIDED that the
disposition of each Purchaser's property shall at all times be within its
control and (b) it is an "accredited investor" within the meaning of Rule 502
of the Securities Act.

                  7. RATIFICATION. Except as amended hereby, all of the
provisions of the Note Agreement shall remain in full force and effect.

                  8. MISCELLANEOUS. This Amendment No. 5 shall be binding
upon and inure to the benefit of and be enforceable by the respective
successors and assigns of the parties hereto, whether so expressed or not.
THIS AMENDMENT NO. 5 SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH AND
GOVERNED BY THE LAW OF THE STATE OF NEW YORK. The headings in this Amendment
No. 5 are for purposes of reference only and shall not limit or

                                       5
<PAGE>

otherwise affect the meaning hereof. This Amendment No. 5 may be executed in
any number of counterparts, each of which shall be an original, but all of
which together shall constitute one instrument.

                    [SIGNATURES APPEAR ON THE FOLLOWING PAGE]

                                       6
<PAGE>

                  If the Purchasers are in agreement with the foregoing,
please sign the form of agreement on the accompanying counterparts of this
Amendment No. 5 and return one of the same to the Company, whereupon this
Amendment No. 5 shall become a binding agreement between the Purchasers and
the Company.

                                       Very truly yours,

                                       ECO SOIL SYSTEMS, INC.

                                       By:
                                          --------------------------

The foregoing Amendment is
hereby agreed to as of the
date hereof.

ALBION ALLIANCE MEZZANINE FUND, L.P.

By:  Albion Alliance LLC,
     its General Partner

         By:
            -------------------------
         Name:  Peter C. Gummeson
         Title: Senior Vice President

PARIBAS CAPITAL FUNDING LLC

By:
    -------------------------
Name:  Jeff Youle
Title: Managing Director

                                       7

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