1 / 30

Crops to be Irrigated

Crops to be Irrigated. Factors for consideration Rooting depth of crop ( Irr. Guide pp.. 3-8,3-9) Are there any soil barriers rock, hard pan, etc. establishment and shallow root depths require more frequent irrigations Crop Height wheel or riser height

tab
Download Presentation

Crops to be Irrigated

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Crops to be Irrigated • Factors for consideration • Rooting depth of crop ( Irr. Guide pp.. 3-8,3-9) • Are there any soil barriers rock, hard pan, etc. • establishment and shallow root depths require more frequent irrigations • Crop Height • wheel or riser height • above canopy or within canopy application • Water tolerance • water sensitive crops develop diseases (beans)

  2. What is Management Allowable Depletion (MAD)? • Mad is defined as the percentage of the available soil water that can be depleted between irrigations without serious plant moisture stress. MAD is expressed as: • a percentage of the total Available Water Content (AWC) the soil will hold in the root zone • a soil-water deficit (SWD) in inches, or • an allowable soil-water tension level • More information Irrigation Guide pg.. 3-7

  3. Example • Given: Silt Loam soil (AWC= 2.1”/ft), growing potatoes with rooting depth of 2.5’and a MAD of 35%. • Find : The maximum amount of water depletion before irrigation is necessary? • 2.1*2.5*.35 = 1.84”

  4. Evapotranspiration Overview • Recently with more weather station and a greater demand for the available water there has been a great push to update ET values. The new ET values are needed to provide a more accurate picture of what is actually happening in the field.

  5. What is EVAPOTRANSPIRATION? • Definition • Evaporation of water from the soil and plant surfaces and transpiration from the stomatal cavities of plants

  6. What are some methods for determining ET? • Estimated crop evapotranspiration ETc • Blaney-Criddle, etc. • Direct measurement • aerodynamic method • detailed soil moisture monitoring • lysimetry • plant porometers • regional inflow-outflow measurements

  7. What influences the method you would select? • Type, accuracy, and duration of available climatic data • Natural pattern of evapotranspiration • Intended use of the evapotranspiration estimates

  8. Climatic Data • Type • Temperature, radiation, wind, humidity • Quality • Length of Record

  9. Natural Pattern of Crop Water Use • Crop ET varies from day to day • Fluctuating climatic • Plant growth • Daily average Vs. average for a period • 1 day Vs 5 day

  10. Frequency Distributions

  11. ET for an Averaging Period

  12. Intended Use • Irrigation Scheduling • System Design • Reservoir operation

  13. Various Methods • NRCS endorses four methods • Penman-Monteith • Radiation method • Temperature Method • Class A evaporation pan

  14. Penman-Montieth Method • More reliable for any length period • daily, monthly, or seasonal • If adequate data available

  15. Radiation Method Not for daily ET, but for average daily ET over a period of days ~ 5day period Good for monthly and Seasonal

  16. Temperature Method ET0 = evapotranspiration for grass reference crop Ce = elevation adjustment factor at = climate adjustment factor bt = climate adjustment factor p = mean daily percent of annual daytime hours T = mean air temperature Not for daily ET, but for average daily ET over a period of days ~ 5day period Good for monthly and Seasonal

  17. Evaporation Pan Method ET0=kpEpan ET0 = evapotranspiration for grass reference crop kp = pan coefficient Epan = evaporation from pan Good for monthly and Seasonal

  18. Things to Consider before changing ET Values • Legal ramifications • Quantity of water supply • System efficiency

  19. SCS TR21 • Where does TR21 fit in? • Water Rights of many States Based on TR21 • Less Accurate

  20. What is the difference between ET0 and Consumptive Use? • CU = Crop coefficient*ET0 • Use reference ET for specific Crop

  21. Crop Curves • NRCS has switched from an Alfalfa based crop reference to a Grass crop reference • To convert use a multiplier factor , usually 1.15 • New ones and procedures found in NEH part 623 chapter 2

  22. Consumptive Use Calculations • Field by field • CU = crop coefficient * ET • Farm CU - multiple fields, multiple crops • weighted CU based on percentage of crops • Project CU • gpm/acre weighted by percent

  23. Weighted Consumptive Use CUw= 80/230*.31+100/230*.21+50/230*.25

  24. Net Irrigation Requirements • Fn = ETc + Aw - Pe - GW - DSW Fn = net irrigation requirement for season ETc = crop evapotranspiration Aw = auxiliary water - leaching, temperature modification, crop quality Pe = effective precipitation GW = ground water contribution DSW= soil water depleted during season

  25. Effective precipitation • The part of rainfall that can be used to meet the evapotranspiration of growing crops. • Does not include surface runoff or percolation below the crop root zone

  26. System Sizing • Simply put Q = Fg*A/t Q = to system flowrate Fg = Gross irrigation requirement A = irrigated area t = time to irrigate the field

  27. What is the difference between Net and Gross? Cg = Cn Ea(1-Dt ) 100 Cg = gross system capacity Cn = net system capacity Ea = application efficiency Dt = system downtime Many efficiencies come in to play Field efficiency Farm efficiency Conveyance efficiency Project efficiency etc. Things influencing Field efficiency Deep percolation Surface runoff Spray, drift losses

  28. Where to get more information • NRCS NEH 623 Chapter 2 “Irrigation Water Requirements”

More Related