Agricultural Irrigation

In recent years irrigators have begun to install variable frequency drives (VFDs) to monitor and control the speed of their irrigation pumps powered by electricity. This has led to several recent questions:

Irrigation-the largest user of freshwater in Nebraska and worldwide-can be applied more precisely.

Use ET Gages and soil moisture sensors to help manage your irrigation this season.

Leaving higher levels of crop residue and doing less tillage can increase the soil water balance by increasing the amount of water that infiltrates the soil from irrigation or precipitation, and decreasing the amount of water that runs off the soil surface. More residue and less tillage also reduce the rate of evaporation of water from the soil. Maintaining residue on the soil surface and doing less tillage can significantly reduce the amount of irrigation water needed to grow a crop.

The goal of irrigation management is to use water in the most profitable way at sustainable production levels. For production agriculture this generally means supplementing precipitation with irrigation. In recent years we have seen declines in groundwater levels, almost statewide. Much of the State of Nebraska is considered fully or over-appropriated. This means that in those over-appropriated areas there will be no new development of irrigated acres.

Nebraska water resources play a major role in the state's heritage and economy. Beginning with the state constitution, Nebraska surface waters have been governed by the Appropriative First-in-Time, First-in-Right Rule which allows diversion of water from the surface waters of the state based upon the date the water right was obtained. Surface water rights entitle land owners or organizations to remove a set amount of water from a specific location.

The University of Nebraska's Bureau of Business Research conducted a study in 2003 to determine the impact of irrigated agriculture on Nebraska 's economy. The net total economic impact was computed by comparing impacts with irrigation to what would have resulted without irrigation. The research examined actual 2003 impacts and what would have occurred if average precipitation had occurred. For normal precipitation the total impact of irrigation would have been just over $3.6 billion per year. Since 2003 was a drought year, the actual economic impact was more than $4.5 billion.

Another major factor in irrigation scheduling is making use of precipitation, both during the growing season and in the off season. Shown below is a map detailing the average net irrigation requirement for corn for the State of Nebraska. The net irrigation requirement is based on precipitation patterns and soils. In wet years less water is needed and in dry years more water will be needed.

Advantages to furrow irrigation include lower initial investment of equipment and lower pumping costs per acre-inch of water pumped. Disadvantages include greater labor costs and lower application efficiency compared to sprinkler and subsurface drip irrigation. The number of furrow irrigated acres in Nebraska has decreased from 2.4 million to approximately 1.5 million acres in the past 10 years.

Harvesting Crop Residues, NebGuide G1846 Issues of crop residue harvest, including nutrient removal and effects on erosion, soil quality, water loss, and yield are discussed in this NebGuide.

Irrigation scheduling needs to begin with a discussion on soil and soil water. This is the basis of irrigation scheduling. Coarse soils, such as sands and gravels, have relatively large pores. However the number of pores is small when compared to a finer textured soil. Fine soils, like clays or clay loams, have relatively small pores. Having many small pores means that a fine textured soil can hold more water than a coarse textured soil.