Soil aggregates associated carbon and enzyme activities under long-term nitrogen and rice straw incorporation in Rice-Wheat system

Intensive tillage and burning or removal of crop residues have led to a decline in soil organic carbon (SOC) content, posing a significant threat to soil quality and global food production. To mitigate this, adoption of conservation-agriculture practices, including residue retention/incorporation, is necessary to promote soil structural stability, increase SOC content, and enzyme activities, and restore carbon (C) sustainability in the rice-wheat system (RWS). Therefore, the long-term effects (10 years) of rice straw incorporation (RS) (0, 5, 7.5, and 10 Mg ha(-1)) and nitrogen (N) levels (0, 90, 120, and 150 kg N ha(-1)) in wheat on soil aggregate associated C pools and enzyme activities were studied. The results revealed that RS incorporation levels of RS7.5 and RS10 had 15.1% and 15.5% higher water-stable aggregates. Within the aggregate fractions, enzyme activities and C pools were significantly higher in the macro-aggregates fraction (Ma-A >0.25 mm) and least in micro-aggregates (Mi-A <0.25 mm). Under Ma-A fraction, treatments RS10 and N-150 had higher enzyme activity compared to RS0 and N-0. Under Ma-A, very labile C, labile C, less labile C, and recalcitrant C were increased by 34%, 25%, 33%, and 48% in RS10 over RS0 and by 20%, 28%, 23%, and 15% in N-150 over the N-0 level, respectively. Thus, the study concluded that the addition of crop residues (7.5 and 10 Mg ha(-1)) along with the N level of 150 kg ha(-1) is a suitable management practice to promote soil structural stability and enzyme activities encouraging long-term SOC sustainability in the RWS.