Aggregate Carbon Pools after 13 Years of Integrated Crop-Livestock Management in Semiarid Soils

Integrated crop-livestock (ICL) systems that utilize perennial or high-residue no-till annual forages may build soil organic matter and, thus, enhance aggregate stability, water retention, nutrient cycling, and C storage. We examined long-term effects of ICL management on soil organic C (SOC) pools compared with continuous cotton [CTN; (Gossypium hirsutum L.)] at the system and individual vegetation levels, both using limited irrigation (65 and 77% replacement of evapotranspiration, respectively). Soil samples collected in 1997 (baseline) and 2010 were fractionated into four water stable aggregate-size classes: macroaggregate (>250 mu m), microaggregate (53-250 mu m), and silt + clay (<53 mu m), and three intra-aggregate size classes: particulate organic matter (>250 mu m), microaggregates (53-250 mu m), and silt + clay (<53 mu m). Reduced tillage and increased vegetation inputs under WW-B. Dahl Old World bluestem [Bothriochloa bladhii (Retz) S.T. Blake; bluestem], a component of the ICL, resulted in increased mean weight diameter (1.5 mm in bluestem vs. 0.40 mm in CTN) and higher proportions of macroaggregates (59%) than under CTN. A continued increase in SOC was measured in the ICL following 13 yr with 22% more SOC relative to CTN. The results from the detailed soil aggregate C fractionation revealed that an ICL under limited irrigation enhanced SOC stored in protected, recalcitrant aggregate pools (intra-aggregate microaggregate SOC of 8.2 and 5.4 mg g(-1) macroaggregate in the ICL and CTN, respectively). These benefits impart important ecosystem services such as potential C sequestration and reduced erosion potential, which are especially important in these semiarid soils.