Soil carbon and nitrogen responses to forage cropping systems following irrigation retirement

Abstract

AbstractLimited annual precipitation and increasing scarcity of irrigation water are forcing farmers in arid and semi‐arid regions to convert irrigated fields into dryland farming, yet their impacts on soil carbon (C) and nitrogen (N) fractions are not fully understood. This study evaluated changes in soil C and N fractions and forage production under four cropping systems after irrigation retirement in a semi‐arid condition. Treatments included an annual winter wheat forage (Triticum aestivum L.) (AWW), a perennial wheat (PW) forage (T. aestivum L. × Thinopyrum spp.) (PW), a mixture of native grasses (NG), and a pasture crop (PC = AWW and NG mixture). Evaluation of various soil C and N fractions, forage dry matter yield, and nutritive value parameters suggested that soil inorganic N and potentially mineralizable N (PMN) were 38%–45% and 36%–44% greater in autumn 2020 and 62%–68% and 46%–55% greater in spring 2021 under AWW and PW, respectively, than NG and PC. Soil potentially mineralizable carbon (PMC) was 58%–129% and 64%–138% greater under NG and PW than AWW and PC. The responses of other soil C and N fractions varied with soil sampling dates but not with crops or crop × sampling date interaction. Total forage dry matter yield was 4016, 7849, 12,517, and 13,869 kg ha−1 for AWW, PW, PC, and NG, respectively, and PW had the best forage nutritive value. These results suggest soil C and N mineralization could be enhanced by adopting perennial systems, including NG, PW, and PC, while PW maintains good‐quality forage production.