Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2014
Publication Date: 1/1/2014
Citation: Caesar, T., Stevens, W.B., Sainju, U.M., Caesar, A.J., West, M.S., Gaskin, J.F. 2014. Soil-aggregating bacterial community as affected by irrigation, tillage, and cropping system in the Northern Great Plains. Soil Science. 179(1):11-20.
Interpretive Summary: Few reports have focused on the microbiological attributes of soil quality related to soil aggregation as influenced by irrigation, tillage, and cropping systems in dryland farming. Sidney, MT ARS researchers compared irrigation, tillage and cropping system effects on aggregate distribution and the community structure of the predominant bacteria that may function as soil aggregators in microaggregates (< 0.250 mm size) at 0-5 cm depth from 2005 to 2008 at a site in western North Dakota. Two irrigation treatments (irrigated vs. non-irrigated) with six management practices that contained malting barley under no-till and conventional tillage and an established no-till Conservation Reserve Program grass-mixture plantation. Study results demonstrated that irrigation and no tillage substantially increased soil macroaggregation and soil stability. Moreover, irrigation and management practices that develop high organic matter at the soil surface favored the growth and survival of specific, beneficial groups of bacteria, in particular Gram negative bacteria in the small microaggregates. These bacteria have been shown to aid soil aggregation in both non-irrigated (dryland) and irrigated conditions at the 0-5 cm depth.
Technical Abstract: Management of irrigated agriculture that influences organic carbon availability can affect soil aggregation in dryland. We compared irrigation, tillage and cropping system effects on aggregate distribution and the community structure of the predominant culturable bacteria that can function as soil aggregators in microaggregates (< 0.250 mm) at 0-5 cm depth from 2005 to 2008 at a site in western North Dakota, USA. Management practices were malt barley (Hordeum vulgare L.) under no-till (BNT) and conventional till (BCT) and an established no-tilled Conservation Reserve Program (CRPNT) plantation consisting of alfalfa and grasses on Lihen sandy loam (sandy, mixed, frigid, Entic Haplustolls), under irrigated (irr) and non-irrigated (nirr) systems. Under irrigation, macroaggregates (4.75-2.00 mm) and mean weight diameter increased in CRPNT and BNT compared with BCT, but in non-irrigated systems only CRP was significantly higher than BCT. Fatty acid methyl ester (FAME) profiling was used to characterize Gram-negative (GN) and positive (GP) bacterial isolates and a soil sedimentation assay to characterize the efficient soil aggregating species. Managements under CRPNTirr and BNTirr significantly influenced the proportions of soil aggregating GN populations, in particular Pseudomonads and Stenotrophomonas maltophilia, compared with the other managements. Species abundance and diversity was the highest in CRPNTirr and BNTirr and the lowest in BCTirr. We demonstrated that irrigation and management practices that develop continuous surface plant residue input significantly increased soil aggregation and drove a specific community structure composed of bacterial populations that can act as soil aggregators in microaggregates of North Dakota dryland at 0-5 cm depth.