The influences of long-term residue and fertiliser management on soil organic carbon (SOC) and related physical properties were investigated in a wheat (Triticum aestivum L.)–corn (Zea mays L.) double-cropping system in the North China Plain. The experiment was initiated in 1981, including 4 treatments: control (no fertiliser); mineral N and P fertilisers; low residue rate plus N and P fertilisers; and high residue rate plus N and P fertilisers. In June 2006, soil samples were taken from the 0–0.05, 0.05–0.10, and 0.10–0.20 m layers to determinate bulk density (ρ_b), water-stable aggregates, bulk SOC, and aggregate-associated C concentrations. Soil water retention curves and saturated hydraulic conductivity (K_s) were measured using samples collected from the 0–0.05 and 0.05–0.10 m layers. The results indicated that residue incorporation significantly increased (i.e. improved) bulk SOC and aggregate-associated C concentration, aggregation, K_s, soil matrix and structural porosities, and water retention capacity. The improvements in soil physical properties by mineral N and P fertilisers alone were limited.

Residue input significantly (P < 0.05) increased the value of S, an index of soil physical quality. A high correlation existed between S and SOC concentration, and the key soil physical parameters, suggesting that S was an effective parameter for evaluation of soil physical quality. Our study concluded that a combination of residue with mineral N and P fertilisers improved SOC concentration, and consequent soil physical quality under the wheat–corn double cropping system.