Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: SUSTAINABLE CROPPING SYSTEMS FOR IRRIGATED SPECIALTY CROPS AND BIOFUELS Title: Response of selected soil microbial populations and activities to land conversion

Authors
item Cochran, Rebecca
item Collins, Harold
item Alva, Ashok

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 14, 2012
Publication Date: July 11, 2013
Citation: Cochran, R.L., Collins, H.P., Alva, A.K. 2013. Response of selected soil microbial populations and activities to land conversion. Communications in Soil Science and Plant Analysis. 44:1976-1991.

Interpretive Summary: A native shrub-steppe ecosystem converted to a series of irrigated agricultural fields was evaluated for several biological indicators that may signal changes in the soil during the initial stages of conversion and disturbance. Soil samples were collected in Grant County, WA in the Columbia Basin from nine sites including undisturbed native shrub-steppe sites and center-pivot irrigated fields with one, two and three years of cultivation. Microbial populations shifted as a result of the conversion from the native to agricultural ecosystem. In addition to the impact of disturbance on soil microbial composition during the transition from a native to an agro-ecosystem, irrigated agro-ecosystems generate soil-litter and environmental conditions very different from the semi-arid native systems. More consistent distributions and types of crop residues in agricultural systems also cause changes in microbial community composition with more diverse supplies of substrates resulting in increased diversity of bacteria.

Technical Abstract: A native shrub-steppe ecosystem converted to a series of irrigated agricultural fields was evaluated for several biological indicators that may signal changes in the soil during the initial stages of conversion and disturbance. Soil samples were collected in the Columbia Basin, WA, USA from nine sites including undisturbed native shrub-steppe sites and center-pivot irrigated fields with one, two and three years of cultivation. Microbial populations shifted as a result of the conversion from the native to agricultural ecosystem. On average, cultivated fields had greater populations of culturable aerobic and pseudomonad bacteria, exhibited greater populations of nitrifying bacteria (105-102), increased nitrification potential, had higher values of microbial biomass nitrogen (MBN) and differed in rates of substrate induced respiration compared to native sites. Many factors including: disturbance and soil mixing from field development, tillage, irrigation, compost amendments, and residue incorporation likely contributed to shifts in soil microbial populations and biomass during conversion. We suggest that differences observed in microbial characteristics were influenced more by the conversion of the native ecosystem to an irrigated agro-ecosystem and the addition of compost than by the length of time of cultivation.

Last Modified: 10/25/2014