Use off-season irrigation more efficiently
By Todd D. Whitney
River Valley District Extension Agent
Water is the most important resource for crop production. Therefore, if water supply needs are met through in-season irrigations, the crop's maximum yield will be reached. However, many irrigators were disappointed when the hot, dry weather caused their 2012 irrigated crop yield to be dramatically lower due to the crop water needs being outpaced by the irrigation system's ability to supply adequate water. According to Loyd Stone, Ph.D., K-State Soil Water Management specialist, reduced well water capacity and lower water tables further provided difficulty for many irrigators to meet the crop's needs strictly from in-season irrigations.
As a result, many irrigators with medium- to fine-textured soils are considering using off-season irrigation in the fall or prior to the next crop being planted. By adding water to the soil profile with these off-season irrigations prior to the growing season, irrigators will "better keep up" with crop demand if the next irrigation season is also extremely hot and dry. These "off-season" irrigation applications can then be a form of insurance.
Stone cautions, though, that recommendations for "off-season" irrigations do not apply to sandier soils with low water-holding capacity.
"Off-season" irrigation recommendations are provide in the new K-State Research and Extension (August 2012) MF3066 publication, "Efficient Crop Water Use in Kansas," which outlines water-holding capacities for varied soils. Off-season irrigations are almost always less efficient than in-season applications, so these irrigations are only recommended if in-season irrigations likely will not keep up with crop water needs.
Water applied during the off-season can be lost due to drainage from the soil profile or through evaporation. This applied water may also become unnecessary if high spring rainfall would have filled the soil profile even without the off-season irrigation.
Efficiency begins to drop off dramatically with off-season irrigations when the percent available water in the soil profile is greater than 60 percent at the application time.
If the soil profile is at 70 to 80 percent of available soil water, off-season irrigation is not recommended, especially in the fall. The efficiency of such an application under these conditions would be very low.
More information on irrigation and water use efficiency is available at the K-State website at http://www.ksre.ksu.edu.