DECOMPOSITION AND NUTRIENT CONTENT OF LITTER IN A FERTILIZED EUCALYPT FOREST

The decomposition and nutrient content of litter was studied for 2 years in regrowth Eucalyptus diversicolor forest to which N (0, 200 kg ha-1 year-1) and P (0, 30, 200 kg ha-1) had been applied. The P addition increased, and the N addition decreased, the rate of dry weight loss of decomposing litter. Analysis of the coefficients of a double exponential decay model with components describing the release of labile and resistant fractions indicated that decomposition of the resistant component of litter was most affected by the fertilizer additions. Treatment with N reduced the rate of loss of this component and increased its half-life by approximately 30%, whereas P treatment increased its rate of decay and decreased its half-life by approximately 30%. P accumulated in litter during decomposition. P uptake and retention was greater in P-treated than untreated plots. The application of N reduced P accumulation in litter. An accumulation of N also occurred during decomposition, the amount of N imported into litter being greater on plots treated with N fertilizer. Treatment with N affected the amount of S in decomposing litter. Litter on N-treated plots either accumulated more S or released it more slowly than litter on plots not treated with N. The application of N as NH4NO3 decreased forest-floor litter pH, increased litter layer mass (by 15%), and increased the amount of N (by 34%) and S (by 32%) stored in the forest floor. Treatment with P reduced the amount of N (by 22%) stored in the litter layer. The application of 200 kg P ha-1 in the absence of N increased the store of P in the litter layer by 80%, but when N and P were applied together the amount of P in the litter was not significantly different between P treatments.