Winter cover crops effects on soil properties and sweet corn yield in semi-arid irrigated systems

Winter cover crops (WCCs) can bolster agroecosystem services, including improving soil and crop yields. However, information is lacking about WCCs in irrigated crops in the semiarid climates of the southwestern United States. We chose three WCC species for their ecological attributes: hairy vetch (Vicia villosa, nitrogen fixation), rye (Secale cereale, nutrient sequestration; allelopathy), and mustard (Brassica juncea, biofumigant). Crops were planted in either monoculture or 2- and 3-way combinations to evaluate agroecosystem services. Sweet corn (Zea mays L.) was planted approximately 2 wk after WCC termination. Neither monocultures nor mixtures consistently produced the most biomass, as WCC biomass production differed between site and year. The highest yielding cover crop was vetch (4302 kg ha(-1)) followed by mustard-vetch (3528 kg ha(-1)) and rye-vetch (3130 kg ha(-1)), all within the same site year, and rye (3016 kg ha(-1)) in another site year. Cover crops generally increased mean weight diameter of soil aggregates (a measure of dry soil aggregation) over time, with values nearly doubling in mustard-vetch and mustard-rye-vetch plots at one site. Wet aggregate stability increased by as much as 18% in mustard and 27% in mustard-vetch plots. Fertilizer requirements decreased compared to fallow plots in the second year in all WCC plots except for rye at one site, and vetch increased sweet corn yield compared to dry fallow plots in 1 yr by an average of 43.1%. These results demonstrate that WCCs can have positive effects on dry aggregate stability and potentially cash crop yield in irrigated, semiarid agroecosystems.