March 22, 2013

With the continued drought in Nebraska, many irrigated producers may be evaluating the benefits of preseason irrigation applications. Many soils across the state have little or no stored soil water, especially at deeper depths. Given this scenario, is preseason irrigation to store soil water for use later in the growing season a good idea?

Background

Considerable research was done on the use of preseason irrigation in the Great Plains in the 1980s and 1990s. The results of this research showed that preseason irrigation is often an inefficient water management practice, with lower water use efficiencies than in-season applications. In addition, Lamm and Rogers (1985) stated that preseason irrigation is a tool that should be used prudently to minimize unnecessary costs and water use. More recently, research on this topic was conducted by Alan Schlegel et al. at Kansas State University from 2006-2009, and Stone et al. at Kansas State University in 2008.

Recent Research

Schlegel’s research was at Tribune, Kansas, which has an average annual precipitation of 17 inches. The study looked at a preseason irrigation of 3 inches performed a month before planting in combination with well capacities and planting populations. (The preseason irrigation amount was designed to move water into the deeper profile.) The well capacities looked at were 245 gpm, 368 gpm, and 490 gpm, which equals 1.9, 2.8, and 3.7 gpm/acre or the ability to apply 0.10, 0.15, or 0.20 inches per day. The three planting populations were 22,500, 27,500, and 32,500. This study was conducted for four years from 2006 to 2009.

Averaged over the four-year study, preseason irrigation of 3 inches increased yields significantly for the two lower capacities, but resulted in only small yield gains for the larger capacity well (Figure 1). When the study looked at the profitability of preseason irrigation using 2010 crop prices of $5.40 per bushel for corn, increases ranged from $50 to $140 per acre for the two lower well capacities, while the higher capacity resulted in a much smaller increase of only $5 to $20 per acre (Figure 2). It is also interesting to note that the higher plant populations resulted in higher yields even at low well capacity. Reducing plant populations is, in most cases, not a profitable technique to use with limited water situations. (See Is a Population Change Warranted in Irrigated Corn? in the March 15 CropWatch.)

Stone’s research at KSU used computer modeling of the soil water balance to estimate the storage efficiency of preseason irrigation. While the study looked at fall and spring preseason irrigation, we will only focus on the spring results. Preseason irrigation can either be held in storage or lost as evaporation or deep percolation. The study found that storage efficiency peaked at 90-95% in the spring when soils were very dry at the time of application. At wetter initial soil water contents, storage efficiency dropped rapidly, especially with soils above 60% available water.

Recommendations

When evaluating the use of preseason irrigation, consider the likelihood of getting precipitation this spring. For example, using High Plains Climate Center records from 1894 to 2012, Hastings has a 70%-85% chance of receiving 2 inches of precipitation during April, and a 40-65% chance of getting 3 inches (Figure 3).

Looking at all of the data, we feel that waiting until May or early June to irrigate would be a better use of irrigation water, especially for those with higher well capacities. By waiting until late May or early June, we keep room in our soils for any precipitation that falls this spring. In addition, low evapotranspiration (ET) rates early in the season would allow us to apply more water than the crop is using, increasing stored soil water deeper in the profile. With the studies showing that preseason irrigation on well capacities of 4 gpm per acre is basically a breakeven, those with higher capacities will see little return to their investment and should avoid preseason irrigation.

For the Panhandle region, the results of the studies in Kansas should closely match what we would expect to see. However, for irrigators with water allocations, using 3 inches before the season would use up a large part of your allocation. Given that in-season irrigation has a higher efficiency, it would be more profitable for those on allocations to wait until later in the season to apply water.

Extrapolating these results to central or eastern Nebraska conditions is difficult given that our typical rainfall amounts are much greater and our ET rates are typically lower. Because of this, it is unlikely that preseason irrigation will be profitable in central and eastern Nebraska, especially on higher well capacities.

The use of monitoring equipment to measure soil water content is recommended for all parts of the state to get a better idea of how much water is present in the soil profile. For more information about tools offered through the Nebraska Ag Water Management Network (NAWMN), please visit water.unl.edu/nawmn.

Summary

In summary, be sure to check your soil profile this spring before determining your irrigation strategy. If system capacity is over 4 gpm per acre, wait until after planting and emergence. If system capacity is less than 4 gpm per acre and soil water is low, start adding some water sooner than normal to partially refill the soil profile to 4 feet. Finally, there is no need to refill deeper than 4 feet unless the crops being grown are alfalfa or wheat.

Sources

A Return Look at Dormant Season Irrigation Strategies. Alan J. Schlegel, Loyd R. Stone, Troy J. Dumler, and Freddie Lamm. Proceedings of the 24th Annual Central Plains Irrigation Conference.

Storage Efficiency of Off-Season Irrigation. Loyd R. Stone, Freddie R. Lamm, Alan J. Schlegel, and Norman L. Klocke. Agronomy Journal. 100:1185-1192.

Aaron Nygren, Extension Educator
Derrel Martin, Extension Irrigation Specialist
Gary Zoubek, Extension Educator
Chuck Burr, UNL Water/Cropping Systems Extension Educator
Bill Kranz, Extension Irrigation Specialist, Northeast REC