Decomposition of Surface Applied and Buried Residue Biomass

The successful utilization of agricultural residues to improve soil quality depends on their management strategy. To improve management decision, there is a need to understand the decomposition dynamics of wide variety of residues under realistic field condition. The objective of this study was to determine the degree of decomposability from surface applied and buried organic residues. On four occasions on a 1-yr field experiment, we determined the decomposition of rice straw, sawdust and wood bark confined in fine mesh litter bags placed on the surface or buried into the soil. Mass loss was measured from the oven dry sample and carbon and nitrogen contents were determined by a CNS auto analyzer. Soil temperature and moisture content were recorded manually on each sampling occasion. The decomposition rate constants were estimated from the observed mass loss by fitting a single compartment exponential decay model. Regardless of the placement effect, the decomposition rate constant, k (d-1) was the highest in straw (0.29), intermediate in wood bark (0.28) and the lowest in sawdust (0.17). The percentage of mass remaining after 1-year of incubation was 92 to 52 for above ground and 78 to 25 for below ground biomass. For both surface and belowground biomass, a significant amount of N was immobilized at the end of incubation period. The C/N ratio declined from 76 to 34, 734 to 442 and 95 to 89 for rice straw, sawdust and wood bark, respectively. The decline in C/N ratio, both with above and below ground biomass, likely associated with an increase in total N during microbial decomposition. The results suggested that, the rate of decomposition and nutrient release is faster for buried and slower for surface applied residue and it is more likely that stored soil moisture rather than temperature regulates residue decomposition.