LAJU PRODUKSI SERASAH DALAM DUA SISTEM BUDIDAYA KARET PADA LAHAN GAMBUT DI KAWASAN RIMBO PANJANG, RIAU

Abstract

The contrasting difference in the vegetation structure of two smallholder rubber growing systems, namely “rubber jungle” and “rubber garden,” has been suspected to affect nutrient cycling in both systems. In this study, we focused on litter production, which roughly reflects the rate of nutrient return to the soil. The objective of the present study has been to assess litter production and composition in both types of rubber growing systems. Our study sites were situated in a peatland area at Rimbo Panjang, Kampar Regency, Riau, where we selected four rubber jungle plots and four rubber garden. Three litter traps (each 1 x 1 x 1 m) were systematically set up beneath rubber stands in a regular interval of 30 m within each selected plot. Trapped litter was collected weekly for 26 consecutive weeks between February and August 2012. Litter samples were dried up to their constant dry weight before weighing and analyzed after their components (leaves, flower and fruits, others). They were also analyzed on a monthly basis for their contents of C, N, P, K Ca, and Mg. In both systems, litter production was strongly correlated with monthly rainfall volume (r2= 0.91 and 0.95in rubber jungle and rubber garden, respectively). Litter production rate was 71.56 g/m2/month or 8587,2 kg/ha/yr in rubber jungle and 65.36 g/m2/month or 7843,2 kg/ha/yr in rubber garden. There was, however, no significant difference between them. Litter averagely consisted of about 60% leaves, 7% flowers and fruits, and 33% other components. Leaf mass varied significantly between rubber jungle and rubber garden, while the mass of flowers and fruits and other components did not. Leaf mass also fluctuated following rainfall, which peaking in March and July. Flower and fruit mass increased from February to August, while the mass of other components decreased during the same period. C/N ratio in litter of both systems influenced by rainfall, in which litter produced during wetter months had slightly smaller C/N ratio, but the correlation between both variables was insignificant. Through litter production trees in both rubber growing systems returned N, P, K, Ca and Mg with the average rate of 125.05 kg/ha/yr, 9.94 kg/ha/yr, 29.71 kg/ha/yr, 77.99 kg/ha/yr and 29.88 kg/ha/yr, respectively