Center Pivot Lateral Move Solid set Planning and Management Considerations Dale Heermann ARS Retired Engineer

Planning Considerations  Field Size  Available water supply  Management ability  Labor availability  Crops to be grown  Soils characteristics  Intake Rate  Water holding capacity

Center Pivot Planning Considerations  Field Size – General needs large areas  Available water supply – meets crop needs  Management ability – Can manage multiple systems  Labor availability – Low labor requirements  Crops to be grown – must clear canopy  Soils characteristics  Intake Rate - runoff potential at outer end  Water holding capacity – can apply small depths

Linear Move Planning Considerations  Field Size – General needs large rectangular areas  Available water supply – meets crop needs  Management ability – Can manage multiple systems  Labor availability – Labor required to move hose  Crops to be grown – must clear canopy  Soils characteristics  Intake Rate - Application rate constant along lateral  Water holding capacity – can apply small depths

Solid set Planning Considerations  Field Size – Can be designed for irregular shapes  Available water supply – meets crop needs  Management ability – Can manage multiple systems  Labor availability – Minimum Labor unless hand move  Crops to be grown – Generally not a limitation  Soils characteristics  Intake Rate - Application rate function of spacing  Water holding capacity – can apply small depths

Area is 4 times larger in outer band Discharge must be 4 times as large Application rate is also higher

Sprinkler selection for center pivot and linear move systems  High Pressure Impact- lower application rate  Low Pressure (sprays, rotators, wobblers)  Spacing and pattern radii affect application rate  In canopy  Truss height  LEPA  Must control runoff – limit to < 1%  Plant in circle for center pivot LEPA  Minimizes soil evaporation  Low capacity – function of water holding capacity

Sprinkler System Capacity Net Irrigation Capacity – Function of Crop ET and precipitation which is function of local conditions Example of reducing capacity by 25% of net irrigation capacity based on soil water holding capacity and Eastern Colorado climatic conditions.  One inch maximum depletion would be exceeded one out of two years.  Five inch maximum depletion would not be exceeded.

EVALUATION OBJECTIVES  Changes Over Time  Installed As Designed  Properly Designed –Nozzle Wear –Pumping Plant Efficiency –Declining Water Table

CURRENT EVALUATION PROCEDURES ASAE STANDARD NRCS PROCEDURE

EVALUATION PROCEDURE BUT A POOR ESTIMATE OF EFFICIENCY PROVIDES AN ESTIMATE OF UNIFORMITY

EFFICIENCY ESTIMATES MUST CONSIDER –IRRIGATION TIMING –RUNOFF –ERRORS IN CATCH CANS 6.2 m/s - 25% (Loss) 2.5 m/s - 5% (Loss)

FIELD PROBLEMS CENTER PIVOT WITH SPRAYS REQUIRES MANY CANS WIND CAN CAUSE ERRORS LABOR INTENSIVE GROOVED OR SMOOTH PADS

TEST EXAMPLE GROOVED PAD TEST FOLLOWED BY SMOOTH PAD TEST Both tests with low wind CU was 10% higher for smooth pad test

SUGGESTED PROTOCOL INVENTORY IRRIGATION SYSTEM –Sprinkler Model –Nozzle Size –Spacing –Pressure –Elevation of Each Tower –Pipe Sizes

SUGGESTED PROTOCOL FIELD MEASUREMENT VERIFY INVENTORY MEASURE - PRESSURE - DISCHARGE

APPLICATION DEPTH NOZZLE PRESSURE COEFFICIENT OF UNIFORMITY CHRISTIANSEN - CU LOW QUARTER - DU OUTPUTS

SIMULATIONS COMPARE SIMULATIONS WITH FIELD MEASUREMENTS OF PRESSURE AND DISCHARGE

SIMULATIONS OTHER BENEFITS Evaluate new designs. Evaluate effect of topography. Use pump curve for change in elevation and drawdown in water table.

CATCH CAN ADVANTAGES VISUAL REAL FIELD DATA SIMPLE TO INSTALL ACCEPTED BY USERS DOES NOT NEED A COMPUTER

DISADVANTAGES (CC) Wind effects Night testing is best Evaporation Grooved pads Large number of cans Labor intensive Extreme care for setup

ADVANTAGES OF SIMULATION Less labor Wind not a problem Complete hydraulic analysis Eliminates catch can error Can be rerun easily for different operating conditions

MULTIPLE RUNS Evaluate multiple designs Analyze effect of changes in drawdown Effects of elevation changes Effect of big gun operation Identify potential problems with nozzle wear, changes in pipe roughness, pumping plant, and water table depth. Effect of pressure regulators

SIMULATION DISADVANTAGES Need pattern shape and radius. Additional data to trouble shoot. Understand models. Difficult to obtain pump data. Difficult to obtain elevation data. Need drawdown water level. Labor to collect field data.

Final Decision Factors and Evaluation  Measurement is absolute necessity  Scheduling is needed for efficiency  Maximum depth to minimize evaporation  Water holding capacity limits depth  Applying more than needed reduces efficiency  Consider differences in soils within field  Crop requirements varies with season  Crops have differing root zone requirements