Water storage and use efficiencies of rainfed winter wheat-summer green manure systems of the US Southern Great Plains

Authors: SINGH, HARDEEP - Kansas State University; Northup, Brian; PRASAD, VARA - Kansas State University

Submitted to: European Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2023
Publication Date: 3/20/2023
Citation: Singh, H., Northup, B.K., Prasad, V. 2023. Water storage and use efficiencies of rainfed winter wheat-summer green manure systems of the US Southern Great Plains. European Journal of Agronomy. 146. Article 126818. https://doi.org/10.1016/j.eja.2023.126818.
DOI: https://doi.org/10.1016/j.eja.2023.126818

Interpretive Summary: Growing winter wheat for forage, grazing and grain is an important activity for agriculture in the U.S. southern Great Plains (SGP). Roughly 16 million acres of winter wheat are planted each year to produce the range of products generated. Wheat is largely grown in continuous rotations without irrigation, with crops separated by periods of summer fallow to conserve moisture for the next wheat crop. However, the wheat-summer fallow system has issues that affect its performance. Among the issues are low efficiencies in using the limited amounts of soil water that is available to grow crops, due to water losses during summer. Conservation practices such as cover crops and no-tillage may help to offset some of the factors that affect wheat-summer fallow systems. These practices can reduce soil erosion, enhance soil biology, store carbon, and increase water use in growing crops rather than allowing losses through evaporation from bare soil. We compared the responses of three winter wheat-summer cover crop (cowpea, pigeon pea, and soybean) rotations to responses of wheat-summer fallow rotations with three different amounts of nitrogen fertilizer [none (as a control), 40, and 80 pounds per acre] applied each year at wheat planting, with the systems managed under both no-till and conventional tillage. We measured grain yields of wheat, and amounts of soil water stored in soils, and used by crops, during 2011 through 2016, to calculate the water storage and use efficiencies of the cropping systems. We found that storage of soil water during summer was reduced by the cover crops, in support of growth by cover crops, and that summer fallow was also inefficient at storing soil water. Grain yield and efficiency of water use by wheat crops were reduced by the cover crops compared to summer fallow, but only during drier years. In wetter years, yields and water use efficiencies of wheat grown in rotation with cover crops were not affected. No-till allowed small improvements in water storage under all treatments, and reduced water losses (by evaporation) during years with wet summers and dry growing seasons of wheat, but did not affect the amounts of soil water that were present. These findings show that growing cover crops during the summer periods of continuous wheat rotations, and using no-till techniques can provide some improvements in available soil water and productivity of wheat in the SGP, during years with average or greater rainfall.

Technical Abstract: Conservation practices such as cover cropping and no-tillage can reduce soil erosion, enhance soil biological activity, increase water storage in soils, and sequester carbon in winter wheat (Triticum aestivum L.)-based production systems. However, cover crops utilize soil water during the summer months, and such water depletion may have negative impacts on subsequent crops of wheat in semi-arid ecoregions where water resources are limited. This study quantified the long-term impacts of tillage systems and cover crops on precipitation storage efficiency (PSE) during summer, precipitation use efficiency (PUE), and grain yield of winter wheat in rainfed production systems. A field study was conducted during five consecutive growing seasons (2011–2016) in the United States (US) Southern Great Plains. Three legumes as summer cover crops (cowpea, pigeon pea, and soybean) were compared with summer fallow and three levels of applied inorganic nitrogen (N) (0, 45 and 90 kg N ha-1) at wheat planting, under conventional and no-till cultivation. Summer PSE was significantly reduced (P<0.05) in response to cover crops, and summer fallow was also inefficient in replenishing soil water. Grain yield and PUE of wheat were significantly reduced (P<0.05) in response to cover crops compared to summer fallow, during dry years; there were no differences during wet or normal rainfall years. No till significantly increased (P<0.05) PSE under all treatments, and reduced evapotranspiration during a subset (either summer or wheat growing season) of all years but did not affect amounts of soil water. Value of the cover crops to offset N fertilizer, in PUE (dollar return per millimeter of precipitation received), was greater than those of summer fallow/inorganic N treatments. Our results demonstrate that replacing summer fallow with cover crops and practicing no till are feasible choices for increasing crop productivity per unit of land and time in the US Southern Great Plains during years with average to above-average rainfall.