Irrigation Measurements and Cost Topic #2073 Megan Burgess

Overview  Amount of water for irrigation  Water measurements  Irrigation costs  Water penetration  Water quality  Water holding capacity  Nitrates  Selenium

Amount of Water for Irrigation  Amount varies with soil, climate, crop, and time to maturity  Replace water lost by transpiration and evaporation  Irrigation principles are simple  Needs of crops vary

Water Measurements  Rainfall reports Water precipitated:  Inches per area such as “acre inch of water”  Totaled annually  If it rained 12 inches of rain in the rainy season, then we had enough water to cover each acre with 1 foot of water

Irrigation Costs  Landowner is charged for each acre foot of water If Grower A uses 1.75 acres feet of water, and the cost is $50 per acre feet, what is the total cost? 1.75 x $50 = $87.50

Irrigation Costs  If a crop requires 32 inches of water to reach maturity, and it rained 12 inches, how much water is added by irrigation? 32 inches - 12 inches = 20 inches water needs to be added if 100% efficient Best efficiency = 85-90%, commonly % efficiency Water would be inches

Water Penetration  Soil should not reach permanent wilting percent before adding more water  With each irrigation depth of water penetration is a little less  Dry soils don’t wet as easy as moist  Water moves through soil at Field Capacity

Water Penetration  Cannot partially wet a soil Small irrigation goes down a short distance  Depth of water penetration can be determined by Tension meters Soil auger Soil-sampling tube

Water Penetration  Typical ranges: Sand - 10 to 12 inches Silt - 6 to 10 inches Clay - 4 to 6 inches

Water Quantity  Quantity varies by Soil moisture content Depth Water holding capacity  Depth of penetration will vary with soil  Some soils hold less than 1 inch of water per foot of soil (others 2 inches)

Water Quantity  Cost of irrigation water will vary with district, fuel to pump, and depth of water being pumped. Water cost may determine crop profitability Sometimes only high-valued crops can be grown profitably with high water costs

Water Holding Capacity  Ability of soil to hold water  Typical capacities:  Sandy -.5 to.75 inches/foot  Loam -.75 to 1.25 inches/foot  Clay to 2.0 inches/foot

Nitrates  Nitrogen fertilizers are soluble and move readily in water  Water carries nitrates deep in soil  If in large quantities of drinking water they are harmful to human health

Nitrates  Factors that influence amount of nitrate movement to groundwater: Amount of nitrate dissolved in soil Rate used by plants Water available for runoff and leaching Soil permeability

Selenium  Sometimes found in areas of agriculture drainage  Nonessential mineral absorbed by plants, too much is toxic  Trace amounts are essential to animal life  Causes “alkali disease” in livestock  Wheat is grown in high selenium areas  Too much will retard plant growth