Rates of decomposition and phosphorus release from organic residues related to residue composition

Abstract

The use of organic residues might be appropriate in maintaining long-term P requirement of crops. Eight plant residues and two manures in a wide range of C : N ratios were incubated for 12 weeks at 25°C, during which the processes of decomposition and formation of acid-extractable P (P release) were assessed. Residues were incubated moist in bags and inoculated with a soil suspension. The exponential model was found to be suitable to describe decomposition and P-release rates from residues. There were two distinct parts of P release in each time curve, which gave two rate constants and were calculated as the slope of each part. The rates of P release of the residues were considerably higher during the first 4 weeks of incubation than during the second phase of incubation (weeks 5-12). Phosphorus release by residues was similar to the decomposition pattern. The residue P content was correlated with P release, but not with decomposition rate. Mass loss and release of P were greater from sunflower and wheat residues than from sheep manure, suggesting that a high C : N ratio does not necessarily retard decomposition. The model parameters of P release were derived which are suitable to estimate the Pfertilizer effect of organic residues. Our results suggest that the use of organic residues as a source for short- and long-term P supply for crops should be encouraged. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.