Research in western Nebraska and eastern Colorado suggests that dryland farmers in the semi-arid Central Great Plains should approach the use of cover crops with some caution.
Many soil health benefits have been associated with cover crops; however, there is little long-term university research data about how well they perform in semi-arid regions such as western Nebraska.
Many of the benefits have been reported in areas that receive more precipitation and have greater humidity than the High Plains region.
To evaluate cover crop use under semi-arid conditions, a two-year study (2012-2013) was conducted at UNL's High Plains Ag Lab near Sidney and at a USDA research station at Akron, Colo. Lead investigators were Gary Hergert, soil and nutrient management specialist, UNL Panhandle Research and Extension Center; David Nielsen, research agronomist, USDA Central Great Plains Research Station at Akron, Colo.; and Drew Lyon, former cropping systems specialist at the UNL Panhandle REC and now professor, Crop and Soil Science Department, Washington State University, Pullman, Wash.
At Sidney cover crops were spring-planted (mid-April) into proso millet stubble in a no-till system under two water availability conditions: rainfed and "average" rainfall. The "irrigated-to-average" rainfall treatments were irrigated every two weeks if additional water was needed to bring the total amount of precipitation for the season up to the 30-year long-term average precipitation.
The cover crop treatments included a 10-species cocktail mix of spring forage peas, lentils, common vetch, berseem clover, oats, spring barley, rapeseed, flax, phacelia, and safflower. For comparison purposes, we chose one species from each of the seed types, that is, legumes (spring forage peas), grasses (oats), Brassicas (rapeseed), and other broadleaves (flax), to plant as single-species cover crops along with the mixture to evaluate the claim that mixtures use less water than single-specie planting. We also included a no-till fallow as a check treatment. The cover crops were terminated (killed with herbicide) around June 20 to allow some soil moisture storage before wheat planting in mid-September.

Figure 1. Soil water depletion from April to June 2012 under cover crops (colored bars) and fallow (white bars), in both dryland and irrigated-to-average precipitation. Soil gained water in fallow fields, but lost water in fields where cover crops were planted and growing during the period.
