Soil organic matter and soil microbial communities in long-term and transitional crop and forage production systems in eastern Wyoming.

摘要

Agricultural systems that meet food and fiber requirements, meet economic goals and maintain agro-ecosystem resilience are valuable in marginally productive semi-arid and cold agroecosystems of the central High Plains of the USA. We (1) reviewed the opportunities and challenges associated with implementing long-term integrated crop and crop-livestock production systems in the central High Plains, (2) evaluated soil organic matter (SOM) and microbial community structure in conventional, organic and reduced-tillage management approaches for cash-crop and forage production systems in irrigated rotations at the Sustainable Agriculture Research and Extension Center near Lingle, Wyoming, and (3) measured the changes in SOM as influenced by long-term historic, conventional, reduced-tillage and no-tillage crop rotations and permanent grasses under the conservation reserve program (CRP) in drylands of eastern Wyoming and western Nebraska, USA.;Review of literature from long-term integrated cash-crop and integrated crop-livestock production systems (Chapter I) revealed that alternative management approaches that include reduced-tillage, certified organic management, or integrating livestock into cropping systems significantly improve soil quality and increase crop production in High Plains region.;On-station evaluation of cash-crop and forage production systems in irrigated rotation during 2009-2012 (Chapter II-V) revealed that organic and reduced-tillage management substantially increased quantity and improved quality of SOM compared to the conventional management approach. Crop rotations combined with alternative management strategies significantly increased the mineralizable, dissolved and microbial biomass SOM. Labile-pool SOM was two to five times greater and microbial biomass assessed using a phospholipid fatty acid analysis (PLFA) was up to 36 times greater in the fourth year of crop rotation than in the first year. The experimental field was under continuous corn for six years prior to the establishment of the experiment. In the cash-crop production system, organic management that included more legume crops and application of manures accrued in the greatest amount of labile SOM and microbial biomass. With the same crop rotations in the forage production systems, the response of reduced soil disturbance was more prevalent than the other management changes. Evaluation of the diversity and relative abundance of nitrogen (N) fixing bacteria (via nifH gene sequencing) revealed significant difference in the relative abundance of N-fixing bacterial phyla. The relative abundance of N-fixing bacteria in the bacterial phyla Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes and Verrucomicrobia varied significantly with crop rotations and management differences. The root biomass, root biomass carbon (C) and N measured only in forage production systems also followed the similar trend as labile C and microbial biomass.;On-farm study of soil organic carbon (SOC) and N in drylands winter wheat production in eastern Wyoming and western Nebraska (VI) indicated significant increase in SOC and N near soil surface as a result of reduced soil disturbance, reduced fallow period and diversified crop rotations. The conventional wheat-fallow rotations that included inputs of fertilizers, however, promoted greater amount of SOC in the 30-60 cm depth.;In conclusion, minimum soil disturbance, more intensive crop rotation and use of organic amendments significantly influence sustainability and resilience of integrated cropping systems and integrated crop-livestock systems. A greater magnitude of change in SOM and microbial properties than previously reported indicates the greater potential for SOC and N sequestration in cold and dry ecosystems with low inherent fertility status than more humid and warmer region.