Carbon and nitrogen properties of particulate organic matter fractions in an Alfisol in the mid-southern, USA

Improved understanding of mechanisms for carbon (C) and nitrogen (N) stabilization is needed to develop new management systems that enhance agricultural sustainability for the intensively cultivated loessial and alluvial soils in the Lower Mississippi River Valley. The distribution of C and N among particulate organic matter (POM) fractions may be key to improving the long-term sustainability of agricultural soils with extensive cultivation histories. The objective of this field study was to evaluate the effects of alternative and conventional agricultural management practices on C and N associated with various POM fractions. In the top 10 cm, following 14 years of consistent management in a wheat (Triticum aestivum L.)-soybean (Glycine max [L.] Merr.), double-crop (WSDC) system on a loessial soil (Glossaquic Fraglossudalf) in eastern Arkansas, averaged across tillage and burn treatments, the coarse-light-fraction C content of the soil was 20.3% greater (P < 0.02) in the irrigated-low- (107.3 g m−2) than the irrigated-high-residue (89.2 g m−2) and 65.4% greater than in the non-irrigated treatment combinations, which did not differ and averaged 64.8 g m−2. Averaged across tillage, burn, and residue-level, coarse-intra-aggregate POM C content of the soil was 46% greater (P < 0.01) in the irrigated (424 g m−2) than in the non-irrigated treatments (290 g m−2). Increasing POM C and N fractions using a combination of conventional and alternative soil and water management practices has the potential for increasing soil C and N storage and maintaining long-term sustainability in intensively cultivated soils.