<PAGE>   1
EXHIBIT 10(x)





                            LONG-TERM INCENTIVE PLAN





                                       Potash Corporation   [POTASH CORPORATION
May 7, 1997                            of Saskatchewan Inc         LOGO]





                                     II-8
<PAGE>   2

                               TABLE OF CONTENTS


<TABLE>
<S>                                                                                                                        <C>
SECTION 1 - PURPOSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1
                                                                                                                         
             1.01    Purpose  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1
                                                                                                                         

SECTION 2 - DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
                                                                                                                         
             2.01    Board  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
             2.02    Committee  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
             2.03    Company  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
             2.04    Employee   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
             2.05    Grant Date   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
             2.06    Plan   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
             2.07    Redemption Date  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
             2.08    Salary   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
             2.09    Target Bonus   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
             2.10    Executive Tiers    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
             2.11    Unit   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
             2.12    Unit Grant Date  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
                                                                                                                          

SECTION 3 - ELIGIBILITY AND PARTICIPATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
                                                                                                                          
             3.01    Eligibility  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
             3.02    Rights Under the Plan  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
             3.03    Subsequent Grant Dates   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
                                                                                                                          

SECTION 4 - UNITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
                                                                                                                          
             4.01    Description and Value of a Unit  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
             4.02    Grant of Units   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
             4.03    Redemption of Units                                                                                  
                     (a)      Part One Units  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
                     (b)      Part Two Units  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
             4.04    Performance Adjustments  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
             4.05    Adjustments  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
</TABLE>
<PAGE>   3

<TABLE>
<S>                                                                                                                       <C>
SECTION 5 - EVENTS AFFECTING ENTITLEMENT  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
                                                                                                                          
             5.01    Termination of Employment  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
                     (a)      Voluntary Termination or Termination for Cause  . . . . . . . . . . . . . . . . . . . . . .  7
                     (b)      Involuntary Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
             5.02    Disability or Retirement   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
             5.03    Death  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
                                                                                                                          
                                                                                                                          
 SECTION 6 - ADMINISTRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
                                                                                                                          
             6.01    Records  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
             6.02    Statements   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
                                                                                                                          
                                                                                                                          
SECTION 7 - RIGHTS OF EMPLOYEES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
                                                                                                                          
             7.01    Non-Assignability  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
             7.02    Rights to Shares   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
             7.03    No Extension of Rights   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
                                                                                                                          
                                                                                                                          
SECTION 8 - ADMINISTRATION AND TERMINATION  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
                                                                                                                          
             8.01    Administration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
             8.02    Amendment  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
             8.03    Termination  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
             8.04    Applicable Laws  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
</TABLE>
<PAGE>   4

SECTION 1 - PURPOSE




1.01         PURPOSE

             The Potash Corporation of Saskatchewan Inc. Long-Term Incentive
             Plan is established as a vehicle by which equity-based incentives
             may be awarded to retain high potential, high value employees, to
             recognize and reward their significant contributions to the
             long-term success of the Company, and to align their interests
             more closely with the shareholders of the Company.
<PAGE>   5

SECTION 2 - DEFINITIONS



In this Plan, the following words, when capitalized have the following meaning:

2.01         BOARD

K            "Board" means the Board of Directors of the Company.

2.02         COMMITTEE

             "Committee" means the Compensation Committee of the Board.

2.03         COMPANY

             "Company" means Potash Corporation of Saskatchewan Inc. and its
             direct and indirect subsidiaries.

2.04         EMPLOYEE

             "Employee" means an employee of the Company designated as a Tier I
             through Tier V executive.

2.05         GRANT DATE

             "Grant Date" means January 1, 1994 and the January 1 every third
             year thereafter, or such other dates as are determined from time
             to time by the Committee and approved by the Board.

2.06         PLAN

             "Plan" means this Potash Corporation of Saskatchewan Inc.
             Long-Term Incentive Plan.
 
2.07         REDEMPTION DATE

             Redemption Date means the date established by the Committee upon
             which Units are redeemed for cash in accordance with Section 4
             (Units).
<PAGE>   6
2.08         SALARY

             Salary means the Employee's base annual salary on the Grant Date
             which amount may, at the discretion of the Committee, be adjusted
             to reflect anticipated changes in actual salary during the life of
             the Units.


2.09         TARGET BONUS

             "Target Bonus" means, in the case of a Tier I Executive 50% of
             Salary;   in the case of a Tier II Executive 40% of Salary; in the
             case of a Tier III Executive 30% of Salary;   in the case of Tier
             IV executive 25% of Salary;   in the case of Tier V Executive 20%
             of Salary.


2.10         TIER I, II,  III, IV OR V EXECUTIVE

             Tier I, II, III, IV or V Executive means an employee of the
             Company designated by the Committee as a Tier I, II, III, IV or V
             Executive.


2.11         UNIT

             "Unit" means a Unit as described in Section 4 (Units).


2.12         UNIT GRANT DATE

             Unit Grant Date means the Grant Date upon which a particular
             number of Units were granted.
<PAGE>   7
SECTION 3 - ELIGIBILITY AND PARTICIPATION




3.01         ELIGIBILITY

             This Plan applies to Employees whom the Committee designates as
             eligible for a grant of Units pursuant to Section 4 (Units).

3.02         RIGHTS UNDER THE PLAN

             An Employee who has been granted Units shall continue to have
             rights in respect of such Units until redeemed for cash as
             described in Section 4 (Units), subject to Section 5 (Events
             Affecting Entitlement).

3.03         SUBSEQUENT GRANT DATES

             A grant of Units to an Employee on a Grant Date shall not be
             construed to create a right to a grant of Units on a Subsequent
             Grant Date.
<PAGE>   8
SECTION 4 - UNITS




4.01         DESCRIPTION AND VALUE OF A UNIT

             A unit is a notional amount equal to the market value of a common
             share of the Company.

             The market value of a common share in respect of a Grant Date or a
             Redemption Date for Employees who receive their salary in United
             States currency shall be the closing value of such a share on the
             day first preceding such date in which a round lot of such shares
             was traded, as listed on the New York Stock Exchange.

             The market value of a common share in respect of a Grant Date or a
             Redemption Date for employees who receive their salary in Canadian
             currency shall be the closing value of such a share on the day
             first preceding such date in which a round lot of such shares was
             traded as listed on the New York Stock Exchange and converted to
             Canadian currency based on the published exchange rate of the Bank
             of Canada in effect on the close of business on the business day
             immediately preceding the Grant Date or the Redemption Date.

4.02         GRANT OF UNITS

             On each Grant Date, the Committee shall grant Units to each
             eligible Employee, using the following formula as a general
             guideline, subject to adjustments approved by the Committee upon
             the recommendation of the chief executive officer of the company.

                            Employee's Target Bonus

                                   DIVIDED BY

                           one Unit on the Grant Date

                                MULTIPLIED BY 3

             The total Units granted shall be divided equally into two parts
             and treated separately for redemption purposes.   Part One Units
             shall be redeemed in accordance with Section 4.03(a) below.   Part
             Two Units shall be redeemed in accordance with Section 4.03(b)
             below.
<PAGE>   9
4.03         REDEMPTION OF UNITS

             Units shall be redeemed for cash at market value on a Redemption
             Date in accordance with paragraphs (a) and (b) below.

             (a)     PART ONE UNITS

                     The Redemption Date for Part One Units shall be determined
                     by the Committee, but in no event shall the Redemption
                     Date be later than the last day of the second calendar
                     year following the calendar year of the Unit Grant Date.

             (b)     PART TWO UNITS

                     One third of the Part Two Units shall be redeemed on or
                     before each of the first, second and third anniversaries
                     of the Unit Grant Date.  The Redemption Dates for Part Two
                     Units shall be determined by the Committee.  In no event
                     shall any Redemption Date for Part Two Units be later than
                     the end of the second calendar year following the calendar
                     year of the Unit Grant Date.

4.04         PERFORMANCE ADJUSTMENTS

                     Notwithstanding Sections 4.01, 4.02 and 4.03 above, the
                     number of Units to be redeemed on a Redemption Date in
                     respect of Part One Units shall be dependent on the
                     performance of the Company and the Employee, based upon
                     criteria determined by the Committee from time to time.
                     Such criteria shall include the cash flow of the Company,
                     the Company's operating results and net income as
                     contained in the most recent financial statements of the
                     Company, and return on equity.  In lieu of the number of
                     Part One Units calculated in accordance with Section 4.02,
                     the Committee may, on or before the Redemption Date,
                     reduce or increase the number of Units redeemable by 50%.

4.05         ADJUSTMENTS

             The number and value of Units held by an Employee shall be
             adjusted to account for divisions or consolidations of the common
             shares of the Company.
<PAGE>   10
SECTION 5 - EVENTS AFFECTING ENTITLEMENT



5.01         TERMINATION OF EMPLOYMENT

             (a)     VOLUNTARY TERMINATION OR TERMINATION FOR CAUSE

                     An Employee who voluntarily terminates employment with the
                     Company or who is terminated by the Company other than in
                     accordance with the  prevailing retirement policy of the
                     Company, for cause (as determined by the Company), prior
                     to retirements, shall forfeit his or her interest in the
                     Units not yet redeemed pursuant to Section 4.03
                     (Redemption of Units).

             (b)     INVOLUNTARY TERMINATION

                     The Units held by an Employee who is involuntarily
                     terminated by the Company, for reasons other than cause,
                     shall be redeemed on the dates set out in Section 4
                     (Units), provided, however, that in addition to the
                     adjustments contemplated in Section 4.04 (Performance
                     Adjustments), the Committee shall reduce the number of
                     Units redeemable pro rata based on the proportion between:
                     (a) the number of months between the date employment
                     terminates and the Redemption Date and (b) the number of
                     months between the Grant Date and the Redemption Date.

5.02         DISABILITY OR RETIREMENT

             The Units of an Employee who becomes disabled and who qualifies
             for benefits under the long-term disability insurance plan
             sponsored by the Company or of an Employee who retires from the
             Company, shall be redeemed in accordance with Section 5.01 (b),
             based on the date benefits commence under the long-term disability
             insurance plan or retirement date, as the case may be.

5.03         DEATH

             The Units of an Employee who dies shall be redeemed in accordance
             with Section 5.01(b), based on the Employee's date of death.
<PAGE>   11
SECTION 6 - ADMINISTRATION



6.01         RECORDS

             The Company shall maintain records indicating the number of Units
             credited to an Employee under the Plan from time to time, the
             Grant Dates of such Units and the market value of a common share
             of the Company on such Grant Dates, as listed on the New York
             Stock Exchange.  Such records shall be conclusive as to all
             matters involved in the administration of the Plan.

6.02         STATEMENTS

             The Company shall furnish annual statements to each Employee
             indicating the number of Units credited to the Employee, the Grant
             Dates of the Units and the market value of a common share of the
             Company on such Grant Dates, as listed on the New York Stock
             Exchange and such other information that the Company considered
             relevant to the Employee.
<PAGE>   12

SECTION 7 - RIGHTS OF EMPLOYEES



7.01         NON-ASSIGNABILITY

             The rights of an Employee under the Plan are non-transferable, in
             whole or in part, in any manner.

7.02         RIGHTS TO SHARES

             This Plan shall not be interpreted to create any entitlement of an
             Employee to the common shares of the Company, or to the dividends
             payable pursuant thereto.

7.03         NO EXTENSION OF RIGHTS

             Nothing contained in the Plan shall give any Employee the right to
             be retained in the service of the Company nor shall it interfere
             with the right of the Company to discharge the Employee.
             Participation in this Plan shall not give any Employee any right
             or claim to any benefit except to the extent provided in the Plan.
<PAGE>   13
SECTION 8 - ADMINISTRATION AND TERMINATION



8.01         ADMINISTRATION

             The Company and the Committee may make such rules as they deem
             necessary or advisable for the administration and operation of the
             Plan.  The Company and the Committee may delegate to any person
             any administrative duties and powers under the Plan.  All
             decisions and interpretations of the Company and the Committee
             respecting the Plan and all rules made pursuant thereto, shall be
             binding on the Company, the Committee and the Employees and their
             respective legal representatives.

8.02         AMENDMENT

             The Board, on the recommendation of the Committee, may amend the
             Plan at any time, provided, however, that no amendment shall
             reduce the interests of the Employees in respect of any Units
             previously granted to an Employee, without the Employee's written
             consent.

8.03         TERMINATION

             The Company may terminate the Plan at any time, in which case all
             Units granted to Employees shall be redeemed in cash as of the
             termination date of the Plan.

8.04         APPLICABLE LAWS

             The Plan shall be governed by and construed in accordance with the
             laws applicable in the Province of Saskatchewan.