Management Systems Impact Soil Aggregate Protected Carbon and Nitrogen.

Soil aggregation is important for physical protection of C and N to sustain agroecosystems. Temporal effects (2001 to 2007) of management systems such as (1) Conventional (no-till with fertilizers and chemicals, CONV), (2) Integrated (reduced tillage with cover crops, manures, fertilizers, and chemicals, INT), and (3) Organic (plowing with cover crops and manures only, ORG) on aggregation and physical sequestration of C and N in soil were evaluated. Soil cores were collected (0-15 and 15-30 cm depth); 2-mm sieved, air-dried and analyzed for various aggregates (0.053, 0.125, 0.25, 0.5, 1 and 2-mm) and their associated C and N, aggregate stability (mean weight diameter, MWD; geometric mean diameter, GMD, and macro- and microaggregate ratios), particulate organic matter C (POC) and N (PON), and total C (TC) and N (TN) contents. Results showed that INT significantly increased macroaggregates and MWD of soil where as ORG increased microaggregates and total N content. The CONV increased PON. Highest concentration of TC was found in 2-mm size aggregate fraction and lowest in 0.125-mm fraction. In contrast, highest concentration of TN was found in 0.5 and 2-mm size fractions compared to lowest in 0.125-mm fraction. The TN was significantly influenced by system x soil depth interaction. The ORG significantly increased TN at surface depth of soil over other treatment combinations. Both POM and PON were significantly higher at surface soil of CONV. Most of the parameters at surface depth of soil were significantly influenced by management systems. Both TC and TN were significantly influenced by management practices over time.