IRRIGATION GUIDANCE FOR PLANNERS

1. IRRIGATION GUIDANCE FOR PLANNERS Rick Schlegel Irrigation Engineer USDA - NRCS

2. FIRST STEP - DO AN IRRIGATION SYSTEM INVENTORY • System capacity or flow available • Conveyance system & condition • Irrigation system types • Crops to be irrigated • Predominate soil types being irrigated • Irrigation water management being practiced by producer

3. AFTER COMPLETING INVENTORY • After the inventory is done, decide if the existing system is adequate or if the irrigator needs to: • Install a new irrigation system • Install flowmeters or chemigation valves • Install a new pipeline or delivery system • Change his cropping system to be more efficient • Manage or schedule irrigation applications • Decommission inadequate wells

4. Let’s break down the inventory and talk about each item

5. SYSTEM CAPACITY • Needs to be large enough to meet crop water needs in a timely manner • RULE OF THUMB FOR PLANNERS: • High water use crops such as corn or peanuts - 7.0 gpm/acre needed • Medium water use crops such as cotton, milo, soybeans – 5.0 gpm/acre needed • Minimum to meet standard – 3.0 gpm/acre

7. PUMP CURVES

9. Conveyance System • Generally use underground PVC • Replace leaky or undersized lines • RULE OF THUMB FOR PLANNERS: Below 400 gpm – 6” PVC 400 – 750 gpm – 8” PVC 750 – 1200 gpm – 10” PVC 1200 – 1700 gpm – 12” PVC • Plan High Pressure Line when delivery system is long length or large elevation increases are encountered

16. COMMON IRRIGATION SYSTEMSUNDER EQIP • LEPA – Low Energy Precision Application • LESA – Low Elevation Spray Application • LPIC – Low Pressure In Canopy • MESA – Mid Elevation Spray Application • Drip System or Microirrigation

17. LEPA SYSTEM

18. LEPA SYSTEM

20. LESA SYSTEM

22. LPIC SYSTEM

24. MESA MESA SYSTEM

26. CROPS AND SOILS • Determine crops to be irrigated • Determine predominate soils to be irrigated • Use Oklahoma Irrigation Guide to gather information for IWM plan • Teach producer how to do Irrigation Scheduling

27. UNDERSTANDING SOIL – WATER – PLANT RELATIONSHIPS

28. TYPICAL CROP ROOT ZONE

29. R A I N F A L L I R R I G A T I O N

30. E V A P O R A T I O N ET EVAPOTRANSPIRATION T R A N S P I R A T I O N DEEP PERCOLATION

31. AVAILABLE WATER CAPACITY (AWC) • THE ROOT ZONE CAN ONLY HOLD SO MUCH WATER ( FIELD CAPACITY ). THE REST IS LOST TO DEEP PERCOLATION. • “AWC” IS THE AMOUNT OF WATER HELD IN THE ROOT ZONE OF THE CROP THAT IS AVAILABLE TO THE CROP.

32. AVAILABLE WATER CAPACITY A W C

33. CLAY, CLAY LOAM & SILTY CLAY LOAM 2.0 IN/FOOT SANDY CLAY LOAM, LOAM, & SILT LOAM 1.8 IN/FOOT FINE SAND AND LOAMY FINE SAND 0.9 IN/FOOT SANDY LOAM & FINE SANDY LOAM 1.5 IN/FOOT

34. MANAGING THE AVAILABLE WATER Using Management Allowable Depletion MAD

35. MAD WATER BALANCE A W C M A D S T I N G Y

36. TWO METHODS PLANNED • 1. Manage the available moisture at 50% AWC • 2. Manage the available moisture to let it drop to the level of a typical producer irrigation plus leaving a one to two inch depletion for rainfall. (1.5” + 1.0” = 2.5”)

37. “MAD” EXAMPLES AT 50% • CROP WITH FOUR FOOT ROOT ZONE: • CLAY, CLAY LOAM, OR SILTY CLAY LOAM AWC = 8.0” MAD WB= 4.0” • SANDY CLAY LOAM, LOAM, OR SILT LOAM AWC = 7.2” MAD WB= 3.6” • SANDY LOAM OR FINE SANDY LOAM AWC = 6.0” MAD WB= 3.0” • FINE SAND OR LOAMY FINE SAND AWC = 3.6” MAD WB= 1.8”

38. AVAILABLE WATER CAPACITY CAN ALSO BE LIMITED BY:

39. AWC PLOW PAN

40. DEVELOPING AN IRRIGATION WATER MANAGEMENT PLAN

46. SCHEDULING IRRIGATION USING EVAPOTRANSPIRATION METHODS

47. Evapotranspiration Methods • Using the Atmometer • Using the Agweather Site on the Mesonet

50. EVAPOTRANSPIRATION USING THE OKLAHOMA MESONET