Long‐term conservation agriculture with moderate nitrogen rate enhances soil labile and total organic carbon through stable aggregate formation

Abstract

Soil physical stability and aggregate‐associated carbon pools are essential for sustaining soil health (SH), yet limited research has explored management impacts on their relationship. Active carbon, or permanganate oxidizable carbon (POXC), an emerging indicator of SH reflecting the labile pool of soil organic carbon (SOC) is sensitive to management practices. This study investigates the simple and interactive effects of variable soil disturbance (strip tillage [ST] vs. conventional tillage [CT]), crop residue levels (high residue [HR] vs. low residue [LR]), and nitrogen (N) fertilization rates (0%, 60%, 80%, 100%, 120%, and 140% of the recommended N), maintained since 2012, on POXC, SOC, total N (TN), and their distribution across various aggregate size fractions (>0.053, 0.15, 0.30, 0.80, and 2.00 mm). Both SOC and TN were highest in ST‐HR‐0% N (23.4 g/kg SOC, 2.78 g/kg TN) and lowest in CT‐LR‐140%N (13 g/kg SOC, 1.26 g/kg TN). POXC varied significantly across treatments, with the highest POXC (632 mg/kg) found under ST‐HR‐80% N, and the lowest (151 mg/kg) under CT‐LR‐140% N. Aggregate size significantly influenced SOC and TN stabilization, with the highest SOC (22.3 g/kg) in 0.30 mm aggregates under ST‐HR and the lowest (12.5 g/kg) in 0.053 mm aggregates under CT‐LR. The ratio of POXC to SOC proved to be a promising metric for evaluating SOC stability within soil aggregates, showing strong correlations with SOC, TN, and aggregate stability. These findings emphasize the potential of combining ST, HR, and moderate N rates (60%–80% N) to enhance soil physical stability and promote POXC retention.