Decomposition and nutrient release from wheat and fababean straw under field conditions

Abstract

The rate of biomass and organic matter loss, and the release of N, P, K, Mg and Ca in decomposing wheat and fababean straw, buried in the soil, were studied for 30 months. The effect of the container type (boxes of 0.8 × 0.8 cm and nylon bags with 0.55-mm diameter holes) in which straw was placed for burial in the soil was also studied. The rate of biomass loss was constant and was not affected by either the straw species or the container type. The proportion of organic matter in the undecomposed biomass was steadily reduced with time and affected by the container type. The rate of loss of absolute quantities of organic matter was linearly reduced with time and for both container types, was higher than the rate of biomass loss in the first 24 months and lower thereafter. Both N and P concentrations in the decomposing material increased with time. Total N and P appeared to be reduced at the end of the experiments but not significantly. The C/N ratio of biomass was reduced with time and affected by the container type, but at the end of the experiments it was still higher than that of the soil. The rate of loss of K, Mg and Ca differed between the two species. For K and Mg, it was more rapid in fababean than in wheat straw at the beginning of decomposition. For Ca, the rate of loss was significant only in fababean straw and was constant.