Soil organic matter and microbial community responses to semiarid croplands and grasslands management

Authors: GHIMIRE, RAJAN - New Mexico State University; THAPA, VESH - New Mexico State University; CANO, AMANDA - US Department Of Agriculture (USDA); Acosta-Martinez, Veronica

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2019
Publication Date: 5/11/2019
Citation: Ghimire, R., Thapa, V.R., Cano, A., Acosta Martinez, V. 2019. Soil organic matter and microbial community responses to semiarid croplands and grasslands management. Applied Soil Ecology. 141:30-37.

Interpretive Summary: Grassland and croplands on the Southern Great Plains are used for cattle grazing; and continued productivity of these systems is important to the sustainability of regional agriculture. However, the role of cattle in soil health and resilience for this region is less clear due to the complex interactions of soil,climate, and agricultural systems involved in every region. A group of scientists from New Mexico State University, and Texas Tech University and USDA-ARS in Lubbock TX evaluated the effects of cattle grazing on the microbial component and soil organic matter in two grasslands (grazed vs. ungrazed) and three croplands (conventional-tilled winter grazed on stubbles; no-tilled and not grazed; and a strip-tilled and not grazed system). Grassland soils had greater soil organic C (18%), total N (13%) than cropland in the top 30 inches of soil , and much greater microbial biomass and enzyme activities of nutrient cycling, especially in the top soil, mainly due to increases in gram-positive bacteria and specific type of fungi. The study suggested that light grazing in croplands and grasslands has the potential to improve soil health for semiarid soils of Southern Great Plains of the US.

Technical Abstract: Livestock integration in cropping systems and conversion of croplands into grazing lands has been increasingly considered to improve agricultural sustainability, yet their roles in soil health and resilience are not clear due to the complex interactions of soil, climate, and agricultural systems. A study was conducted to evaluate the effects of cropland and grassland management systems on soil organic carbon (SOC) and total nitrogen (N) across the soil profile (0–20, 20–40, 40–60, and 60–80 cm) and microbial community size, structure, and activity in the soil surface (0–20 cm) as indicators of soil health. Cropland systems compared included conventional-tilled winter grazed cropland (CTGC) and no-tilled and strip-tilled croplands (NTC and STC) without livestock grazing. Grassland systems included grazed grassland (GGL) and ungrazed grassland (UGL). Grassland soils accumulated 18% greater SOC and 13% greater total N than cropland soils in the 0–80 cm profile. Microbial community size (sum of ester-linked fatty acid methyl esters [El-FAME]) in the surface 0–20 cm was 90% greater, and enzyme activities were 131–155% greater in the grasslands than in the croplands. Within grasslands, cattle (Bos taurus) grazing increased microbial community size by approximately 42%, which was mainly due to greater fatty acid methyl esters (FAME) markers for gram-positive bacteria (51%) and Actinobacteria (73%). Grazed cropland had 95% more ß glucosaminidase activity than ungrazed croplands. This study suggests light grazing and grassland restoration has potential to improve soil health and resilience through an increase in SOC and microbial community responses related to nutrient cycling.