Response of soil organic matter to cover cropping in water-limited environments

Authors: THAPA, VESH - New Mexico State University; GHIMIRE, RAJAN - New Mexico State University; VANLEEWEN, DAWN - New Mexico State University; Acosta-Martinez, Veronica; SHUKLA, MANOJ - New Mexico State University

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2021
Publication Date: 1/15/2022
Citation: Thapa, V.R., Ghimire, R., Vanleewen, D., Acosta Martinez, V., Shukla, M. 2022. Response of soil organic matter to cover cropping in water-limited environments. Geoderma. 406. Article 115497. https://doi.org/10.1016/j.geoderma.2021.115497.
DOI: https://doi.org/10.1016/j.geoderma.2021.115497

Interpretive Summary: Cropped soils on the Southern High Plains (SHP) have low organic matter/soil carbon, low fertility and microbes compared to other regions in the nation because of the region’s low precipitation (less than 20 inches ), high temperatures (>90F for several months), and extreme droughts. Cover crops can increase nutrient cycling and soil organic matter/carbon with potential benefits to soil health, soil water conservation, and enhanced soil microbes recovery from extreme droughts. Researchers in New Mexico State University and USDA-ARS of Lubbock Texas found that oat and a mix of pea and canola encouraged microbial activity compared to other cover crops. Among different size soil aggregates, largest amounts of carbon and nitrogen were stored in aggregates of small size, suggesting an increase in carbon sequestration in these soils due to cover crops. The research suggests using oat or pea and canola in combination as cover crops for the SHP region to increase soil carbon and the benefits associated with those increases.

Technical Abstract: Cover cropping has the potential to improve soil health and resilience in semiarid regions by increasing labile soil organic carbon (SOC) and N pools that enhance functions related to soil organic matter (SOM) dynamics, biological activity, aggregate stability and distribution, and nutrient cycling. This study evaluated the response of selected soil health indicators for SOM dynamics to the introduction of different cover crops to a limited-irrigation winter wheat (Triticum aestivum L.)-sorghum (Sorghum bicolor L. Moench)-fallow rotation. Soil samples were collected in the summer of 2019 and 2020 from 0-15 cm depth of each plot established in fall 2015. Our cover cropping treatments included pea (Pisum sativum L.), oat (Avena sativa L.), canola (Brassica napus L.), and mixtures of pea + oat (POmix), pea + canola (PCmix), pea + oat + canola (POCmix), and six-species mixture (SSmix) of pea + oat + canola + hairy vetch (Vicia villosa Roth) + forage radish (Raphanus sativus L.) + barley (Hordeum vulgare L.) and a fallow. Principal component analysis (PCA) identified that SOC, pH, total N, POC, and mineral-associated organic carbon (MAOC) were more sensitive to cover cropping treatments. Spring cover crop biomass was 26 to 76% greater with oat, POmix, POCmix, and SSmix than pea, canola, and PCmix as cover crops. Soil inorganic nitrogen (N) was 7 to 36% lower with cover crops than fallow. Oat and PCmix had 41 to 69% greater 72h-carbon dioxide-carbon (CO2-C) than fallow, canola, POmix, and SSmix at termination time. Thirty-six days after termination, particulate organic carbon (POC) content was 3 to 73% greater with pea than other treatments. The SOC and total N contents were 10 to 22% greater with oat than a pea, canola, POmix, and SSmix. The SOC and total N concentrations were higher in intermediate size aggregates (250µm-2mm and 53-250µm) than other size fractions. The SSmix and oat increased wet aggregate stability (WAS) by 41 to 43% than fallow. Our study showed that oat could be an alternative cover crop to improve the most SOC and total N with important implications to soil health and resilience of cropping systems in semiarid environments.