Inorganic fertilizer enrichment of soil: effect on decomposition of plant litter under subhumid tropical conditions

Litter decomposition is controlled by many factors, including the quality o f the litter and conditions within the soil environment. The decomposition and N and P release from prunings of three agroforestry plant species (Sesb ania sesban, Croton megalocarpus, and Calliandra calothyrsus) were evaluate d on field plots which were amended with: (1) no fertilizer (control), (2) 120 kg N ha(-1) applied as urea (urea), and (3) 150 kg P ha(-1) applied as triple superphosphate (TSP) over a period of 77 days. For all litters, the percentage of initial mass, N and P remaining (dry weight basis) over time followed the single exponential model and was strongly influenced by the in teraction of plant species and fertilizer. Decay rate constants (k) of loss of litter mass (k(B)), and release of N (k(N)), and P (k(P)) varied among litters and fertility regimes. The ks, kw and kp of Sesbania and Croton wer e enhanced more by urea than by TSP and control treatments. For Calliandra, k(B) with TSP was higher (0.016 day(-1)) than with urea (0.012 day(-1)) an d control (0.012 day(-1)), Sesbania and Croton showed no differences in k(B ), k(N) and k(P) between control and TSP. For Sesbania and Croton, leaching may have accelerated the release of P to meet the needs of decomposer orga nisms, resulting in no significant effects of TSP on their decomposition pr ocesses. The low rate of decomposition of Calliandra may be partly due to i ts high lignin content. In conclusion, the higher the total N or P of litte r, the less likely would be the significant effects of additions of the ino rganic form of fertilizer on the decomposition processes.