Impact of long-term manuring and cropping system on stability of humus associated with clay-organic complex

ABSTRACT The objective was to study the impact of ten year’s manuring and fertilization on chemical stability of clay-organic complex (COC) in rice−potato−wheat (R–P–W) and maize−potato−onion (M–P–O) cropping systems. Soil samples were collected from the control, 100% NPK–Fertilizer, 100% N–Vermicompost (VC), 50% NPK–Fertilizer + 50% N–VC, 100% NPK–Fertilizer + crop residue (CR), 100% N–VC + CR. The stability (1/k) of humus C i.e. inverse of humus desorption rate constant (k) in hours (h), in COC was higher in 100% N–VC an1d 00% N–VC + CR in both the cropping systems. The C:N ratio of humic acid (HA) was also higher in the treatments receiving full organics (100% N–VC and 100% N–VC + CR) and showed positive correlation (p < 0.05) with the humus C stability in COC. Long-term manuring treatments created C = N and C–O stretching of aromatic ether in HA extracted from 100% NPK–VC and other selected treatments in both the cropping systems. 100% N–VC and 100%N–VC + CR produced higher stability of humus-C in Inceptisol. The R–P–W imparted higher stability of humus C than M–P–O cropping system.