Mass Loss and C and N Release from Decomposing Fresh and Composted Residues as Affected by Cold Climate Conditions

Information on the decomposition and nutrient release pattern of fresh and composted residues under low temperature field conditions is still limited. A 540-day period litterbag study was conducted in an agricultural field of the northeastern Japan to quantify mass loss and C and N release from fresh (rice straw and sawdust) and composted (compost) residues. Decomposition rates (k) were estimated from mass loss data by fitting a single-pool exponential decay model for actual days of field incubation. The k values were also expressed in degree-days (DGD) and decomposition-days (DCD) time scales to account for the effect of temperature and precipitation on residue decomposition. At any time scales, k values followed the order: compost > straw > sawdust. Daily mass loss, C and N release were significantly affected by residue type and incubation time. Compost showed higher decomposability and potential N source, while a considerable amount of N was immobilized in straw and sawdust decomposition. Mass loss was positively correlated with initial C content and C: N for compost and straw, while it was negatively correlated with initial N content for straw and sawdust. Decomposition exhibited at a slow rate even at sub–zero air temperature during soil freezing conditions, indicating that residue decomposition under cold climate field conditions may be more regulated by moisture availability than temperature per se.