Significant Management Impacts On Intra-Aggregate Soil Fractions.

Soil organic matter (SOM) and carbon (SOC) pools, influenced by agricultural management (tillage intensity, irrigation, and crop selection), are important drivers of ecosystem functioning including impacts on the global C cycle. Alternative practices (integrated crop livestock systems; ICL) have been shown to conserve water, maintain profitability, and enhance soil quality when compared to continuous cotton (CTN). Two separate studies investigated soil quality factors [mean weight diameter (MWD), soil aggregates, and SOC content] in four ICLs and three CTN systems, initiated between 1997 and 2007. The initial study focused on changes over 13-years and differences between an ICL (no-till rotational crops and perennial grass) and a conventional CTN system. The second study examined impacts of three ICL and two CTN systems on soil quality factors. Greenhouse gas (GHG) fluxes were measured in two ICL systems from the second study. The initial study indicated that CTN combined with wheat cover crop maintained SOC content over 13 years; however, C-sequestration potential was enhanced by no-till rotational cropping or conversion to perennial pasture. Specifically, the ICL system increased whole (31%) and intra-aggregate (40%) SOC pools. MWD was reduced 60% and 47% under CTN and rotational crops, respectively, while perennial grass increased MWD by 50%. Within the second study, ICLs (including perennial vegetation) resulted in the greatest C-sequestration potential with up to 130% more SOC in the intra-aggregate microaggregate fraction. Overall, SOC in intra-aggregate fractions was greatest with incorporation of ICLs when compared to CTN production. Additionally, increased SOC may partially offset the greater GHG fluxes measured in perennial components. With greater aggregate stability (i.e., increased MWD) and SOC content, particularly in protected pools, ICls resulted in the greatest potential for improved C-sequestration and soil quality. These factors are important when producers design agroecosystems to meet specific goals and potential soil and water resource limitations.