Irrigation Management 101 Steve Melvin University of Nebraska - Extension

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1 Irrigation Management 101 Steve Melvin University of Nebraska - Extension

2 Why Irrigate Irrigation increases yields and profitability Managing precipitation variability Higher and more consistent yields allows for better planning of input levels (fertilizer, pesticides, labor, farm equipment, etc) and expenses to optimize returns. Managing the irrigated cropping system is key Crop residue on the soil surface will conserve water Pride and satisfaction of a good crop each year

3 Managing Precipitation Variability Every year is different Demand for food, fiber, and bioenergy crops is the same each year Irrigation helps stabilize the year to year difference in production Inches Precipitation Variability Scottsbluff, NE ( ) Falls City, NE ( ) Inches

4 Corn Yield Increases Rainfed vs Mechanized Irrigation 200 Bushels/Acre Irrigated Year Source Missouri 2004 Irrigation Survey, University of Missouri Agricultural Extension Program Dryland

5 Corn Yield Response to Total Applied Water Data from Irmak and Rathje Plant growth and yield as affected by wet soil conditions due to flooding or over-irrigation. University of Nebraska NebGuide G1904

6 Wheat Yield Response to Total Applied Water Grain Yield (kg/ha) Irrigation + precipitation (mm) Data from Zhang et al Management of supplemental irrigation of winter wheat for maximum profit. Food and Agricultural Organization of the United Nations

7 YIELD FOR PIVOT-IRRIGATED CORN IN SOUTHWEST NEBRASKA 250 WELL WATERED YIELD = 220 bu/acre GRAIN YIELD, bushels/acre DEPTH OF IRRIGATION APPLIED, inches

8 GRAIN YIELD PER UNIT OF WATER, bushels/acre-inch YIELD INCREASE PER INCH OF WATER WITH PIVOTS INITIAL YIELD INCREASE = 13 bu/ac-in (most of water goes to ET) DEPTH OF IRRIGATION APPLIED, inches

9 Energy Balance at the Earth s Surface REFLECTED RADIATION EXTRATERRESTRIAL RADIATION ADVECTION wind SOLAR RADIATION LONG- WAVE RADIATION SOIL HEAT SOIL Source-University of Nebraska Lincoln-Extension

10 SOIL WATER BALANCE IRRIGATION RAIN TRANSPIRATION EVAPORATION ROOT DEPTH UPWARD FLOW STORED SOIL WATER GROUND WATER RUNOFF DEEP PERCOLATION Source-University of Nebraska Lincoln-Extension

11 Soil Water Terms Saturation Field Capacity More Available Less Available Permanent Wilting Point Source-University of Nebraska Lincoln-Extension Zero Water Content

12 SAT % 50% 0% FC MB PWP Water in soil (in/ft) Sand Loam Silty Clay Loam

13 Saturation Field Capacity Minimum Balance Wilting Point Source-University of Nebraska Lincoln-Extension

14 Inches of Water per 60 Days Hydraulic Conductivity Inches of water per 60 days Field Capacity 70% of Available Water This chart created with data from the Soil Water Characteristics, a computer program developed by Keith Saxton, USDA ARS Centabar

15 Soil Water Movement in/day The soil water recharges from the top to the bottom in/day 1.0 in/year

16 Soil Water Movement A soil profile that is completely filled from rain or over irrigation can deep percolate a lot of water in/day

17 Soil Water Movement in/day 1.0 in/year Typical in-season irrigated soil water levels with the top, 3 rd & 4 th foot wet and the second foot fairly dry in/day

18 Soil Water Movement Water needed to recharge soil if top four feet are at 40% of available water (dryland fields may easily hold twice this amount of water in the typical 6 ft root zone). Soil Type Sand 2.4 Loam 4.8 Silty Clay Loam 4.3 Water, In

19 PRECIPITATION CHANGES ABOUT 1 INCH FOR EVERY 25 MILES EAST-WEST From Nebraska Dept. of Natural Resources

20 1998 Yield Map Elsie Fully Watered Water Miser BMP Farmer Deficit

21 Evapotranspiration Deficit Impact on Corn Yield Graph from Crop Water Management, AGLW Water Management Group, FAO

22 Republican River Basin Irrigation Management Project Summary Six Year Average of Corn Yields by Management Strategy and Site. Management Strategy Soil WHC 1 FARM Fully Water Deficit (in/ft) Watered Miser BMP Site Average Yields (bu/acre) Arapahoe 2.1" Elsie 1.5" Dickens 2 1.0" Benkelman 1.8" North Platte 3 2.0" McCook 2.0" All Sites Percent of FARM Yield Soil Water Holding Capacity. 2 Data for Dickens not included in 97 due to irrigation error & soybeans in FARM management strategy not used in North Platte. 4 Yield and applied water are weighted by the number of years of data at each site.

23 Republican River Basin Irrigation Management Project Summary Six Year Average of Corn Water Use by Management Strategy and Site. Soil WHC 1 FARM Fully Water Deficit (in/ft) Watered Miser BMP Site Applied Water (acre-inches/acre) Arapahoe 2.1" Elsie 1.5" Dickens 2 1.0" Benkelman 1.8" North Platte 3 2.0" McCook 2.0" All Sites Percent of FARM Applied Water Soil Water Holding Capacity. 2 Data for Dickens not included in 97 due to irrigation error & soybeans in FARM management strategy not used in North Platte. 4 Yield and applied water are weighted by the number of years of data at each site.

24 Republican River Basin Irrigation Management Project Summary Average of Corn Yields and Water Use by Management Strategy and Site Management Strategy Fully Water Water Miser Def. Site Average Yields (bu/acre) Holbrook Culbertson Holdrege Curtis Arapahoe Loomis Bartley All Sites Percent of Fully Watered Yield Site Applied Water (acre-inches/acre) Holbrook Culbertson Holdrege Curtis Arapahoe Loomis Bartley All Sites Percent of Fully Watered Applied Water Yield and applied water are weighted by the number of years of data at each site.

25 Example 100 acres field to be planted to corn 490 ac-in of water to be used this year Fully Watered 400 ac-in/7.1 in = 56 acres 56 acres (Fully Watered) * 198 bu/a = 11,155 bu 44 acres (Dryland) * 90 bu/a = 3,960 bu Total 15,115 bu Deficit Irrigate 400 ac-in/4.0 in = 100 acres 100 acres * 188 bu/a = 18,800 bu Deficit irrigation produced 3,685 bu more corn

26 The four keys to making the Water Miser BMP work are: Invest in soil moisture monitoring equipment and use it Critically evaluate when to start irrigating Keep good rain and irrigation application records and compare them to what the ET has been for the field Starting at the dough stage, calculate the amount of rain and irrigation that is needed to get the crop to maturity

27 Normal water requirements for corn between various stages of growth and maturity in Nebraska Stage of growth Corn Approximate number of days to maturity Water use to maturity (inches) Blister (R2) a Dough (R4) Full dent (R5) ¼ milk line ½ milk line ¾ milk line Physiological maturity (R6) NebGuide G1871 Predicting the Last Irrigation of the Season

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29 Monitor the Pressure and / or Flow Rate One of cheapest ways to monitor your machine Know what the pressure should be If pressure is wrong, system can t be right. Flow meters, use them for management Source-University of Nebraska Lincoln-Extension

30 Example of Nozzling Problems with Pivots Good Uniformity Leak End-gun Adjust Nozzles Switched If sprinklers not properly installed / maintained high efficiency is not possible Rogers et al, 2009

31 Aerial Photos Tell Story of Nonuniform Water Distribution

32 Why Should I Want To Do Irrigation Scheduling? To know when to start for the season Water Miser Strategy saves 1-2 inches of water To know when to irrigate during the irrigation season Variation in rainfall, crop water use, and well capacity-may use more some years and save a lot on other years (-2 to 10 inches) To know how soon to begin delaying the start of the next irrigation to use up the stored soil water by crop maturity Save 2 to 5 inches

33 Irrigation Management 101 Steve Melvin University of Nebraska - Extension