Soil profile carbon, nitrogen, and crop yields affected by cover crops in semiarid regions

Cover crops are increasingly adopted to improve soil health in arid and semiarid regions, yet their effects on soil profile organic carbon (C) and nitrogen (N) and crop yield are inconsistent. We evaluated the cover crop effect on soil organic C (SOC) and N (SON) contents and water-filled pore space to a depth of 0.8 m and crop yield in a winter wheat (Triticum aestivum L.)-sorghum (Sorghum bicolor L. Moench)-fallow rotation under limited-irrigation conditions. Cover crop treatments were fallow (no cover crop), pea (Pisum sativum L.), oat (Avena sativa L.), canola (Brassica napus L.), pea-canola mixture, oat-pea mixture, pea-oat-canola mixture, and a six-species mixture including pea, oat, canola, hairy vetch (Vicia villosa Roth), forage radish (Raphanus sativus L.), and barley (Hordeum vulgare L.). Five years of cover cropping (2016-2020) did not affect SOC storage. Soil organic N at equivalent soil mass (ESM) layer 0-2500 Mg ha(-1) was 8-14% greater in fallow than other treatments, except pea and oat-pea mixture. The fallow treatment also had 54-156% and 11-72% higher inorganic N content than cover crop treatments at ESM layers of 2500-5000 and 5000-7500 Mg ha(-1), respectively. Sorghum grain yield was 33-97% higher following fallow and oat as cover crop than other treatments in 2020. Although there was a variation in crop yield responses, cover cropping largely did not affect soil profile C and N contents under a limited-irrigation semiarid cropping system.