Spatiotemporal Magnitudes and Trends of Cover-Crop Evapotranspiration in Nebraska, Iowa, and Kansas

Abstract

Although some benefits of growing cover crops have been recognized in agricultural production fields, wider adoption of these rotational crops requires quantitative information on actual evapotranspiration (ETa) in different climatic gradients, which is currently very limited. This study quantifies, maps, and evaluates the magnitudes and trends of cover-crop growing season (September–April) ETa in Nebraska, Iowa, and Kansas during 2005–2016. Data sets from 76 weather stations in 3 states and representing 297 counties, comprising 559,360 km2 land area, are used to quantify and map spatial distribution of cover-crop growing season ETa, air temperature, and precipitation. Precipitation had a strong east-to-west decreasing trend; cover-crop growing season precipitation in the study region varied from 121 to 540 mm. Air temperature had a north-to-south increasing trend, with cover-crop growing season mean air temperature varying from −3°C to 16°C. Seasonal total ETa exhibited a southwest to northeast decreasing trend, ranging from 267 mm in Finney County in southwest Kansas to 148 mm in Floyd County in northeast Iowa, with a study region mean seasonal ETa of 207 mm. The highest monthly ETa was observed in September for all states, and minimum values were observed in December and March. These spatial maps of monthly cover-crop ETa are some of the first in the literature and can serve as an important tool for assessing the feasibility of growing cover crops in terms of water resources availability, use, planning, and management.