Soil Nutrient Flux in Relation to Trenching Effects under Two Dipterocarp Forest Sites

Abstract

The standing stock and annual flux of soil macro-nutrients were studied under two dipterocarp forest sites one in a dipterocarp plantation and other in a lowland dipterocarp forest of Peninsular Malaysia. We measured the chemical properties of soils and the standing stock of the soil macro-nutrients such as available P, exchangeable (ex-) K, ex-Na, ex-Mg, ex-Ca, total C and total N of soil profiles taken from a depth of 50 cm. The annual flux of inorganic ions at a soil depth of 20 cm was estimated for ammonium-N, nitrate-N, phosphate-P, Na, K, Mg and Ca using the ion exchange resin (IER) core method. Cores of IER was buried under the trenched and untrenched sites of two forest sites for a year in order to clarify the soil-plant interactions in soil nutrient dynamics. The C/N ratio was higher in the plantation forest (11 to 14) than in the lowland forest (8 to 11). Total exchangeable cations of the plantation and lowland forest soils were 4.5 kmol (+) ha-1 and 5.9 kmol (+) ha-1, respectively. The annual flux rate of cations and anions in the plantation forest was 2.97 kmol (+) ha-1 yr-1 and 1.12 kmol (+) ha-1 yr-1 for the untrenched sites and 2.79 kmol (+) ha-1 yr-1 and 2.16 kmol (+) ha-1 yr-1 for the trenched sites. In the lowland forest, those figures were 5.06 kmol(+) ha-1 yr-1 and 0.08 kmol (+) ha-1 yr1 for the untrenched sites and 3.27 kmol (+) ha-1 yr1 and 0.30 kmol (+) ha-1 yr-1 for the trenched sites. Trenching caused decreases in cation flux both in the plantation and lowland forests. But Mg flux increased in the plantation forest and ammonium-N flux showed no drastic changes at any of the sites. On the other hand, trenching increased the anion flux in both forests. We will discuss the effects of trenching treatment on nutrient dynamics in soil system of tropical rain forest.