Mulch decomposition under agroforestry conditions in a sub-humid tropical savanna processes and influence of perennial plants

For the effective use of mulch materials in tropical agriculture and agroforestry knowledge of the speed of decomposition and nutrient release is of primary importance. The transfer of these informations from one site to another requires comparability of the processes of decomposition and their intensity at the two sites. In a litterbag experiment the decomposition and release of main nutrients from leaves and branches of Cajanus cajan (L.) Millsp. were investigated with regard to the underlying physical and biological processes during an 81 days period. To test the influence of perennial plants on the decomposition process, the study was conducted on an agricultural field in 1.1 m, 6.9 m and 14.9 m distance from a tree and hedge band. During the first 11 days leaching was high, especially for N and P (about 50% lost) and K (75–80% lost). After the 11th day consumption of the mulch material by the soil fauna was the dominating process of decomposition. During this phase the perennial plants significantly retarded the decomposition of Cajanus branches, but not leaves, probably by their influence on termite activity. Ca release was also retarded in leaves. After about 6–7 weeks, more than 90% of all main nutrients except Ca had been released from the samples. To minimize nutrient losses from nutrient-rich mulch materials, they should be applied repeatedly in small quantities according to the nutrient demand of the crop.