INFLUENCE OF IRRIGATED AGRICULTURE ON SOIL CARBON AND MICROBIAL COMMUNITY STRUCTURE

Authors: Entry, James; FUHRMANN, JEFFRY - UNIVERSITY OF DELAWARE; Sojka, Robert; SHEWMAKER, GLENN - UNIVERSITY OF IDAHO

Submitted to: Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2004
Publication Date: 3/23/2004
Citation: Entry, J.A., Fuhrmann, J.J., Sojka, R.E., Shewmaker, G.E. 2004. Influence of irrigated agriculture on soil carbon and microbial community structure. Environmental Management. 33(Supplement 1):S363-S373.

Interpretive Summary: Increasing the amount of carbon in soils is one method to reduce the concentration of carbon dioxide in the atmosphere. We measured organic carbon stored in Southern Idaho soils having long term cropping histories that supported native sagebrush vegetation, irrigated moldboard plowed crops, irrigated conservation -chisel- tilled crops and irrigated pasture systems. Carbon dioxide emitted as a result of fertilizer production, farm operations and carbon dioxide lost via dissolved carbonate in irrigation water, over a 30 year period, was estimated, and used to calculate net carbon fixation. Organic carbon in ecosystems decreased in the order irrigated pasture, irrigated conservation tillage, irrigated moldboard plow and native sagebrush. In February 2001, active fungal, bacterial and microbial biomass was greater in irrigated pasture soils than all other soils. In August 2001, active bacterial biomass was greater in irrigated moldboard plowed soils than the other soils. Active fungal biomass was greater in irrigated pasture soils than all other soils. Whole soil fatty acid profiles from the native sagebrush soils were distinct from the agricultural treatments and contained greater amounts of total fatty acids than the other treatments. Whole soil fatty acid profiles from irrigated pasture soils suggest that arbuscular mycorrhizal fungi are more common in these soils than soils from the other treatments. Irrigated arid soils can both increase carbon storage while also increasing microbial biomass and changing microbial diversity.

Technical Abstract: Increasing the amount of carbon (C) in soils is one method to reduce the concentration of carbon dioxide in the atmosphere. We measured organic C stored in Southern Idaho soils having long term cropping histories that supported native sagebrush vegetation (NSB), irrigated moldboard plowed crops (IMP), irrigated conservation -chisel- tilled crops (ICT) and irrigated pasture systems (IP). Carbon dioxide emitted as a result of fertilizer production, farm operations and carbon dioxide lost via dissolved carbonate in irrigation water, over a 30 year period, was estimated, and used to calculate net C fixation. Organic C in ecosystems decreased in the order IP>ICT>>IMP NSB. In February 2001, active fungal, bacterial and microbial biomass was greater in IP soils than all other soils. Active fungal, bacterial and microbial biomass was least in ICT soils at the 15-30 cm depth than all other soils. In August, 2001, active bacterial biomass was greater in IMP soils than IP, ICT and NSB soils. Active fungal biomass was greater in IP soils than all other soils. Whole soil fatty acid profiles differed among management regimes, depth and sampling dates. Fatty acid profiles from the NSB soils were distinct from the agricultural treatments and contained greater amounts of total fatty acids than the other treatments. The IMP and ICT soils yielded fatty acid profiles that were similar to each other, although the 15-30 cm depth was distinct from all other treatment-depth combinations. Fatty acid profiles from the IP soils suggest that arbuscular mycorrhizal fungi are more common in these soils than soils from the other treatments. In general, irrigated arid soils can both increase C storage while also increasing microbial biomass and changing microbial diversity.