Nutritional Environment of Tropical Peat Soils in Sarawak,Malaysia Based on Soil Solution Composition

It has been considered that natural peat soils and swamp forest ecosystems in the tropics are quite oligotrophic. This concept seems to be related to the low mineral contents in the soil solid phase of the peat soils. However, some nutritional elements such as K, Mg, Ca, and/or P may be abundant in the soil solution phase and could easily migrate in peat soils. In order to analyze the nutritional environment of peat soils, chemical composition of the soil solid phase and soil solution was compared.

This study was carried out in Naman Forest Reserve, Sibu and in/around Sg. Talau Peat Research Station, Mukah, Sarawak, Malaysia. In both areas, each of the three study sites with a different depth of underlying mineral layer was selected for sampling of soil and soil solution. All the soils studied except for one shallow peat profile were classified into Oligotrophic peat based on Fleischer’s criteria. The soil solution collected monthly showed the following characteristics in its composition.

1. Concentrations of Al, Si, and Fe were higher in the soil solution from the shallow peat than in that from the deep peat, reflecting the effect of underlying mineral layers on the soil solution composition.

2. Concentrations of Na, Mg, and Cl in the soil solution and Na and Mg contents in the soil solid phase reflected the distance from the sea. In the Naman series, accumulation of K and Ca in the soil solution was larger in the surface layer in the deep peat than in the shallow peat, though such clear trend was not observed for the K content in the soil solid phase.

3. The concentrations of N and P were fairly high in the soil solution in all the profiles except for P in the profile near the center of the peat dome. Dissolved P consisted mostly of ortho-phosphate, whereas a larger part of N was in the organic form.

4. At the Sago plantation farm on deep peat, depletion of K and P was observed during the rainy season. Such instability in the concentrations in the soil solution was attributed to forest clear-cutting and subsequent disturbance of nutrient cycling.

In general, the concentrations of N, P, K, and Ca in the soil solution were not low even in the Oligotrophic peat. However, in taking account of the fact that the peat soils showed low mineral contents in the available forms and that the bulk density was also quite low, the potential capacity to supply K, Ca, and/ or P was not necessarily high in spite of the apparent high intensity observed for the soil solution composition. Therefore, from the viewpoint of nutrient dynamics, the potential for the use of reclaimed peat land was considered to be rather limited especially under low input management.