Carbon Sequestration in Soil Aggregates Under Irrigated and Dryland Cropping Systems in a Semi-Arid Area.

 

ABSTRACT

This study was conducted to evaluate the effect of irrigation and dryland cropping systems on soil aggregation and physically protected soil organic carbon (SOC) stocks in a semi-arid region. Aggregate size distribution, total C and N concentrations for the aggregate size fractions [macro (M) and micro (m) aggregates, and silt & clay fractions] and for the isolated fractions from macroaggregates [coarse particulate organic matter (cPOM), microaggregate into macroaggregate (mM) and Silt&Clay-M] were measured in soils from full irrigation alfalfa (Full-A), full irrigation corn (Full-C), limited irrigation forage alfalfa (Ltd-fA), limited irrigation forage corn (Ltd-fC), limited irrigation grain wheat (Ltd-gW), limited irrigation grain corn (Ltd-gC), dryland wheat (Dry-W) and dryland corn (Dry-C) treatments. The amount of free microaggregates comprised 69.4 to 75.6 % of soil and the macroaggregates comprised less than 18 % of the soil. The latter was higher under full irrigation corn (Full-C), limited irrigation forage corn (Ltd-fC) and limited irrigation grain corn (Ltd-gC) compared to dryland corn (Dry-C). The SOC stock in the mM fraction was higher under full irrigation crops relative to dryland crops especially in corn treatments. Conversion from full irrigation to dryland induced a reduction in macroaggregates. Full-C treatment had higher SOC stock in mM fraction relative to Dry-C. Our study indicates that irrigation and no-till management enhance aggregate formation and increase C sequestration in mM fractions compared to dryland cropping system.