<PAGE>



                                  EXHIBIT 10(a)

Certain confidential portions of this Exhibit were omitted by means of redacting
a portion of the text indicated by two asterisks "**". This Exhibit has been
filed separately with the Secretary of the Commission with the redacted text
pursuant to the Company's Application Requesting Confidential Treatment under
Rule 24b-2 of the Securities Exchange Act of 1934.


    LINDSAY MANUFACTURING CO. MANAGEMENT INCENTIVE PLAN (MIP) 2003 PLAN YEAR

1. PURPOSE

The purpose of the Management Incentive Plan (the "Plan") is to:

Encourage performance consistent with the Company's business strategy

Focus on near-term performance results as well as progress toward the
achievement of long-term objectives

Strengthen the link between performance and pay by delivering awards based on
measurable corporate and individual goals.


2. DEFINITIONS

The terms used in this Plan have the meanings set forth below.

"Company" shall mean Lindsay Manufacturing Co.

"Compensation Committee" shall mean the Compensation Committee of the Company's
Board of Directors.

"Corporate Performance Component" shall mean the portion of a Participant's Plan
award that is based on the Company's financial performance as defined in Section
7.

"Individual Performance Component" shall mean the portion of a Participant's
Plan award that is based on a Participant's performance relative to individual
objectives established in accordance with Section 7.

"Named Executive Officers" shall mean the executives of the Company listed in
the Executive Compensation section of the Company's Proxy Statement.

"Participant" shall mean a key employee eligible for awards under the terms
outlined in Section 4 of this Plan.

"Plan" shall mean Lindsay Manufacturing Co. Management Incentive Plan.


3. EFFECTIVE DATE

The Plan shall be effective as of September 1, 2002 and will be in effect for
the 2003 bonus year. The 2003 bonus year is defined as September 1, 2002 through
August 31, 2003.


4. ELIGIBILITY FOR PARTICIPATION

Participation in the Plan is limited to individuals in positions which have
significant responsibility for and impact on the Company's corporate
performance.

Only the Chief Executive Officer and those employees in grades E through G are
eligible to be considered for participation in the Plan.



                                       19
<PAGE>

Participation in the Plan does not guarantee or entitle any employee to
participate in any bonus plan enacted in the future. Participation in the Plan
at any target bonus level does not guarantee or entitle any employee to be
eligible to participate at any similar target bonus level in any bonus plan
which may be enacted in the future.


5. ENROLLMENT IN THE PLAN

Initial Enrollment

At the beginning of the Plan year, each Participant must be enrolled in the Plan
subject to the approvals and eligibility criteria set forth in Sections 4 and 6.
The enrollment process is as follows:

Plan Participants will participate in the Plan at the standard target percent
per grade level as listed in Section 6.

The Company's Chief Executive Officer will review the participant list and
projected bonus costs of enrolled employees with the Compensation Committee. The
Compensation Committee provides final approval on the aggregate potential cost
of the Plan.

Mid-year Enrollment

When hiring or promoting employees during the Plan year who may be eligible for
participation in the Plan, the following procedures must be followed:

Prior to the commencement of the recruiting or promotion process, the hiring
manager consults with Human Resources to determine the position's eligibility
for participation in the Plan and the recommended target bonus amount.

Offer letters indicating bonus Plan participation and target bonus award
opportunities to new hires and/or promoted employees must be reviewed by the CEO
or, in the case of a Named Executive Officer, by the Compensation Committee.
Target bonus recommendations must be approved before communication to a
prospective Participant. Generally, employees hired or promoted during the
fourth quarter 2003 are not eligible to participate in the 2003 Plan.

6. DETERMINATION OF TARGET PAYOUT LEVELS

Incentive awards will be calculated as a percentage of the Participant's actual
base salary received during the Plan year. While award amounts will vary based
on the range of award opportunity and an assessment of individual performance
results, the target award opportunities for each grade level are shown below:

<Table>
<Caption>
      GRADE      TARGET % OF SALARY
      -----      ------------------
<S>              <C>
      CEO        60%
      G          35%
      F          25%
      E          15%
</Table>

Actual participation is subject to approval by the CEO, or in the case of a
Named Executive Officer, by the Compensation Committee. Actual participation is
based on an assessment of the individual's position impact on the organization.
Standard target percents per grade level should be followed for all Plan
Participants.

If a Participant's Plan target award opportunity (Target % of Salary as set
forth above) changes due to promotion into a grade level with a higher target
bonus, the Participant's bonus will be calculated based on his or her actual
salary during the Plan year and a weighted average bonus percentage. The
weighted average bonus percentage will reflect the portion of the Plan year
spent in each grade level (e.g., seven months at 15% and five months at 25%). In
evaluating the performance of Participants who change positions during the Plan
year, consideration will be given to the length of time and results in each
position. Actual award decisions will be made by the CEO or, in the case of a
Named Executive Officer, by the Compensation Committee. Generally, fourth
quarter promotions will not result in an increase in a Participant's target
award opportunity.



                                       20
<PAGE>


The CEO will review and approve award recommendations for all employees other
than Named Executive Officers prior to payout. Final approval authority for all
payments (except for award payments to the Named Executive Officers) rests with
the CEO. Individual award payments for all Participants (except the Named
Executive Officers) may be adjusted at any time and for any reason at the
discretion of the CEO.

The Compensation Committee will determine the award payments to the named
Executive Officers.

Award payments will be calculated on an annual basis and paid in accordance with
the Company's normal payroll cycle. Payments will be made during the first
quarter following the Plan year. The payment date may be changed at any time and
for any reason at the discretion of the CEO, or in the case of a Named Executive
Officer, with approval of the Compensation Committee.


7. BASIS OF AWARDS

Measurable performance objectives for each Plan Participant will be established
at the beginning of the Plan year (or at mid-year for mid-year hires or newly
eligible employees). In 2003, consideration will be given to:

Corporate Performance Component: Company performance vs. Plan performance
objectives in accordance with Section 7.

Individual Performance Component: Participant's performance relative to
individual goals established in accordance with Section 7.

Individual and Corporate Performance Components will be added to reach a
Participant's total bonus. The relative weighting will vary by grade in
accordance with the following schedule:

<Table>
<Caption>
                          CORPORATE          INDIVIDUAL
        GRADE             PERFORMANCE        PERFORMANCE
        -----             -----------        -----------
<S>                       <C>                <C>
        CEO               80%                20%
        G                 80%                20%
        F                 65%                35%
        E                 50%                50%
</Table>

At the beginning of the Plan year, the objectives for the Corporate Performance
Component are identified. For the 2003 Plan year, payouts under the Corporate
Performance Component will be determined based on the Company's Operating Income
growth. Performance against these goals is assessed at year-end to determine if
Threshold Company performance has been achieved to trigger bonus payments.

For 2003, the following performance levels have been established for Threshold,
Target, and Potential performance:

<Table>
<Caption>
                                Threshold       Target        Potential
                                ---------       ------        ---------
<S>                             <C>             <C>           <C>
        Operating Income           **             **              **
</Table>

Recommended award amounts may range from 0 - 200% of the Corporate Performance
Component of the Participant's target award, based on Company performance.

Percentages between the points in this matrix will be interpolated.

In the event of an acquisition, revenue and operating income resulting from the
acquisition will be excluded from award payout calculations, unless the CEO or
Compensation Committee suggests a modification to the objectives under the
Corporate Performance Component that would incorporate revenue and income
generated as a result of the acquisition, and the Compensation Committee
approves the modification.

The Individual Performance Component will be based on written objectives set
annually for Participants by their supervisors and approved by the CEO or, in
the case of a Named Executive Officer, by the Compensation Committee. Objectives
will be based on the Participant's position and may be financial, operational or
strategic.


                                       21
<PAGE>

Objectives under the Individual Performance Component may be linked to
team-based goals, if appropriate.

Examples of appropriate objectives under the Individual Performance Component
include:

Safety
Customer Service
Market Share
On-time Delivery
Cost Reduction
Product Development

Recommended award amounts may range from 0% - 200% of the target amount under
the Individual Performance Component. Recommended award amounts will be based on
an assessment of the individual's performance relative to objectives established
under the Individual Performance Component, in accordance with the following
guidelines:

<Table>
<Caption>
                                                 PAYOUT
     INDIVIDUAL                                  (AS  % OF  TARGET  INDIVIDUAL  PERFORMANCE
     PERFORMANCE                                 COMPONENT)
     -----------                                 ------------------------------------------
<S>                                              <C>
     Does not meet objectives                    0%
     Meets some objectives                       50%
     Meets most objectives                       75%
     Meets all objectives                        100%
     Exceeds objectives                          150%
     Significantly exceeds objectives            200%
</Table>


The "Payout (as % of Target Individual Performance Component)" represents the
payout relative to target award for the Individual Performance Component of the
Plan.


8. CHANGES IN EMPLOYMENT STATUS

Under most circumstances, Participants who cease to be employees of the Company
during the Plan year or after the Plan year but prior to the date of actual
payment will receive no award. Only active employees on the date that the bonus
is paid will be eligible to receive an award. Any exceptions will require the
approval of the CEO, or in the case of a Named Executive Officer, the
Compensation Committee.

In the event that a Participant transfers out of an eligible position into an
ineligible position within the Company, the employee may be eligible for a
prorated bonus award based upon the approval of the CEO, or in the case of a
Named Executive Officer, the Compensation Committee.

In all cases awards will be calculated and paid according to the provisions in
Sections 6 and 7 of this Plan document.


                                       22
<PAGE>



9. ADMINISTRATION

General authority for Plan administration and responsibility for ongoing Plan
administration will rest with the Compensation Committee of the Company's Board
of Directors. The Compensation Committee has sole authority for decisions
regarding interpretation of the terms of this Plan.

The Company reserves the right to amend or change the Plan in whole or in part
at any time during the Plan year. Amendments to the Plan require the approval of
the Compensation Committee.

Participation in the Plan does not constitute a contract of employment nor a
contractual agreement of payment. It shall not affect the right of the Company
to discharge, transfer, or change the position of a Participant. The Plan shall
not be construed to limit or prevent the Company from adopting or changing, from
time to time, any rules, standards or procedures affecting the Participant's
employment with the Company or any Company affiliate, including those which
affect bonus payouts.

If any provision of this Plan is found to be illegal, invalid or unenforceable
under present or future laws, that provision shall be severed from the Plan. If
such a provision is severed, this Plan shall be construed and enforced as if the
severed provision had never been part of it and the remaining provisions of this
Plan shall remain in full force and effect and shall not be affected by the
severed provisions or by its severance from this Plan. In place of any severed
provision there shall be added automatically as part of this Plan a provision as
similar in terms to the severed provision as may be possible and be legal, valid
and enforceable.

This is not an ERISA plan.  This is a bonus program.





                                       23