Cover crop biomass and species affect soil microbial community structure and enzymatic activities in semiarid cropping systems

Authors: THAPA, VESH - New Mexico State University; GHIMIRE, RAJAN - New Mexico State University; Acosta-Martinez, Veronica; MARSLIS, MARK - New Mexico State University; SCHIPANSKI, MEAGAN - Colorado State University

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2020
Publication Date: 8/31/2020
Citation: Thapa, V.R., Ghimire, R., Acosta Martinez, V., Marslis, M.A., Schipanski, M. 2020. Cover crop biomass and species affect soil microbial community structure and enzymatic activities in semiarid cropping systems. Applied Soil Ecology. 157:103735. https://doi.org/10.1016/j.apsoil.2020.103735.
DOI: https://doi.org/10.1016/j.apsoil.2020.103735

Interpretive Summary: The use of cover crops has been suggested as means to improve soil health in agricultural systems. One way to track changes in soil health after adopting new management practices is by analyzing soil microbes and their activities. Scientists from New Mexico State, USDA-ARS in Lubbock TX, and Colorado State University evaluated different cover crops (barley, canola, forage radish, oat, pea, and different mixtures of them) in a semiarid soil with limited irrigation during 2017 and 2018. Planting oat as a cover crop, significantly increased fungal populations when compared to fallow. This is important because fungi are beneficial microbes that can increase soil aggregation and nutrient availability for plant growth. Moreover, most cover crops increased enzyme activities associated to carbon and nitrogen availability for plant growth. Overall, results from this study demonstrate that cover cropping has the potential for improving soil health in a hot semiarid zone near New Mexico.

Technical Abstract: Cover crops are promoted to increase soil organic carbon (SOC) storage and improve soil biological health in agricultural systems. However, cover crop effects on soil microbial communities – key regulators of SOC and nutrients – and functioning are not clear in semiarid environments. This study investigated the response of soil microbial community structure and enzyme activities to cover crop integration under limited-irrigation winter wheat (Triticum aestivum)-sorghum (Sorghum bicolor)-fallow rotation. The study had a randomized complete block design with eight treatments and three replications. Treatments were pea (Pisum sativum); oat (Avena sativa); canola (Brassica napus L.); and mixtures of pea + oat (POmix), pea + canola (PCmix), pea + oat + canola (POCmix), and pea + oat + canola + hairy vetch (Vicia villosa) + forage radish (Raphanus sativus L.) + barley (Hordeum vulgare L.) (diverse-mix) as cover crops; and a fallow. Soil samples were collected in the summer of 2017 and 2018 from 0 to 15 cm depth of each plot established in fall 2015. Microbial community size and structure were evaluated via ester-linked fatty acid methyl ester (EL-FAME) analysis, which showed that total microbial community size and fungal community were similar between soils under oats and diverse-mix, and were 31% and 41% greater than fallow, respectively. The FAME marker for arbuscular mycorrhizal fungi (AMF) was 84% greater under oats than fallow. The combined enzyme activity of acid phosphatase, ß-glucosidase, and ß-glucosaminidase was 294 mg p-nitrophenol (PNP) kg-1 soil h-1 under diverse-mix, which was greater than fallow (204 mg PNP kg-1 soil h-1, p = 0.021) in 2018. Cover cropping during fallow period in a crop-fallow rotation could increase total microbial community size, fungal abundance, and enzyme activities associated with carbon (C) and nutrient cycling. Among cover crops, oat and its mixture with legumes (pea and hairy vetch) and brassicas (canola and forage radish) were most effective in improving soil health and biogeochemical cycling in a hot and dry semiarid climate.