MSU Extension Irrigation

Table of Contents

Introduction..................................................................................................................................... 5
Background and Recent Research................................................................................................... 7
Objectives........................................................................................................................................ 8
Study Area and Systems Description............................................................................................... 8
Methodology and Equations........................................................................................................... 9
Results and Discussions................................................................................................................. 12
Fertigation based on Uniformity ................................................................................................... 18
Recommendations......................................................................................................................... 18
Acknowledgements....................................................................................................................... 23
References..................................................................................................................................... 24
Appendix A .................................................................................................................................... 25
Appendix B..................................................................................................................................... 30
Appendix C..................................................................................................................................... 36

Introduction

Center pivot irrigation systems are invented over 60 years ago to reduce labor requirements, enhance agricultural production, and optimize water use. According to USDA Farm and Ranch Irrigation Survey in 2008, center pivot irrigation are used on
the majority of sprinkler-irrigated land in United States and represent 83% from all types of sprinkler systems.

A center pivot consists of a lateral circulating around a fixed pivot point. The lateral is supported above the field by a series of A-frame towers, each tower having two driven wheels at the base.

Water is discharged under pressure from sprinklers or sprayers mounted on the laterals as it sweeps across the field or suspended by flexible hose over the crops. The lateral line is rotated slowly around a pivot point at the center of the field by electric motors at each tower.

Uniformity of a system is a measure of its ability to apply the same depth of water to every unit area. Without good uniformity, it is impossible to irrigate adequately and efficiently; parts of the field will be either over-irrigated or under-irrigated. Three uniformity measurements are to be considered in the evaluation; Coefficient of Uniformity (CU) and Distribution Uniformity (DU) and Potential Application Efficiency of Low Quarter (PELQ).

A CU rating of 90%-95% is considered excellent and would only require regular maintenance.

85%-90%% is considered good and would not need major adjustments; regular maintenance and inspection are required.

80%-85% the system requires inspection and sprinkler package check.

80% or less the system requires an adjustment to the sprinkler package, change the default system, sprinkler pressure and conduct full maintenance for the whole system.

The CU accounts for the increased area covered by each sprinkler as you move further from the pivot center. Sprinklers near the end gun cover greater acres than those close to the center pivot.

compares the lowest quarter of the water depth caught to the entire set of data from the catch cans. DU is useful as an indicator of the magnitude of the distribution problems. DU is calculated by dividing the weighted average of the lowest 25% of the catch cans by the weighted average of the entire catch cans.

A DU of 85% or greater is considered excellent, 80% is considered very good, 75% is considered good, 70% is considered fair, and 65% or less is considered poor and unacceptable.

Potential Application Efficiency of Low Quarter (PELQ) is a measure of how well the system can apply water if management is optimal. PELQ is the ratio of the lowest 25% weighted average depth in the catch cans to the average applied rate that is obtained from the flow rate, revolution time, and wetted area. In this way deep percolation losses would be kept to minimum. Low PELQ values indicate design or management problems.

PELQ should be determined in order to evaluate how effectively the system can utilize the water supply and what the total losses may be. It is, therefore, a measure of the best management practice and should bet thought of as the full potential of the system.