Aggregate size distribution and associated carbon and nitrogen in mulched winter wheat and spring corn

The influence of surface mulching on soil aggregation and associated carbon (C) and nitrogen (N) varies by mulching materials and crop types. The 6 yr effect of straw mulching (SM), plastic film mulching (PM), and no mulching (CK) on soil aggregation and associated C and N concentrations at 0–20 and 20–40 cm soil layers were studied under dryland winter wheat (Triticum aestivum L.) and spring corn (Zea mays L.) in the Loess Plateau of China. Regardless of crop types, aggregate proportion was greater in macroaggregates (2.00–10.00 mm), but lower in microaggregates (<0.50 mm) with mulching than without in both soil layers. The mean weight diameter of aggregates was greater with SM and PM than CK. Compared with CK and PM, SM increased soil organic C (SOC) and total N (STN) concentrations in both macroaggregates and bulk soil at 0–20 cm. Aggregate proportion and soil C and N concentrations at both depths were more pronounced in winter wheat than spring corn. The recovery rates of bulk soil SOC and STN in aggregates varied from 94% to 107%. Straw and plastic film mulching enhanced soil aggregation compared with no mulching. Straw mulching was more effective in increasing SOC and STN concentrations at the surface layer in dryland winter wheat and spring corn.