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

Authors: Paye, Wooiklee; LAURIAULT, LEONARD - New Mexico State University; ACHARYA, PRAMOD - New Mexico State University; GHIMIRE, RAJAN - New Mexico State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2023
Publication Date: 12/8/2023
Citation: Paye, W.S., Lauriault, L.M., Acharya, P., Ghimire, R. 2023. Soil carbon and nitrogen responses to forage cropping systems following irrigation retirement. Agronomy Journal. https://doi.org/10.1002/agj2.21523.
DOI: https://doi.org/10.1002/agj2.21523

Interpretive Summary: Many farmers in semiarid regions including the United States Southern High Plains (SHP) are under immense pressure to transition to dry-land farming due to limited rainfall and depletion of groundwater resources. Irrigated croplands in semiarid regions often have more organic carbon and better soil health than dry-lands. Thus, the transition to dry-land farming is expected to reduce soil organic carbon and deteriorate soil health, affecting crop productivity and ecosystem sustainability in semiarid regions. A two-year study evaluated the effect of annual versus perennial cropping systems as two transition strategies on soil health and forage supply for the livestock industry of the SHP. Perennial cropping systems such as native grasses and perennial wheat resulted in greater soil organic carbon than annual winter wheat and pasture cropping -- a mixture of annual wheat and native grasses. The total forage dry matter yield over two years was significantly greater under native grasses, pasture crops, and perennial wheat than annual wheat, and perennial wheat had the greatest overall forage nutritive value than other cropping systems. The study results suggest that transitioning to perennial cropping provides an opportunity to mitigate the potential decline in soil health and crop production associated with the transition from irrigated to dry-land cultivation under semiarid environments.

Technical Abstract: Limited 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.