Biomass and nutrient stocks of fallow vegetation in Southeast Sulawesi, Indonesia

The biomass and nutrient stocks of 2-, 3-, 4-, 5-, 6-, 8-, 10- and 15-year-old fallow vegetation were determined in abandoned slash-and-burn fields in SE Sulawesi (Indonesia) to analyse their relation to fallow and to recommend alternatives for a sustainable resource use. The biomass was studied in 14 different fallow vegetation stands of the Amasara and Buke region, both located in Kendari regency, while the nutrient stocks were determined from the nutrient concentrations (leaves+wooden part) of 13-20 selected species of the fallows in the Buke region, contributing 80 to 92% to the total biomass. According to the fallow age, the total biomass of the fallow vegetation ranged from 11 to 235 t/ha, corresponding with nutrient stocks 123-1180 kg N per ha, 9-110 kg P per ha, 113-1610 kg K per ha, 75-1315 kg Ca per ha, and 28-270 kg Mg per ha. The variability of the biomass within the stands increased with an increase in fallow age. In a 4-5-year fallow period, sufficient biomass can be produced in the fallowed area to provide plant material for an adequate mulch layer for the subsequent cropping period. Also, the nutrient stocks of the 4-5-year-old fallow vegetation were sufficient for 1-2 cropping periods, provided that land preparation does not include burning which causes substantial nutrient losses by volatilization.