Ultisols of "Lowland Dipterocarp Forest" in East Kalimantan, Indonesia : II. Status of Carbon, Nitrogen, and Phosphorus

Status of C, N, and P including available N and P was studied in 35 Typic Paleudults and Typic Hapludults under a "Lowland Dipterocarp Forest" in East Kalimantan, Indonesia. The total C, N, and P contents decreased abruptly within the top 15-20 cm layers. The contents were directly correlated with the clay content in each horizon group. The higher C, N, and P contents in the finer soils were considered to be associated with the stabilization of organic matter by clay particles and with the higher mobility of organic matter in the finer soils. The content of available N which was directly correlated with the total N content. The N availability was the highest when the C : N ratio ranged between 10 and 15. Nitrification was not as pronounced as ammonification. The available P content was well correlated with the total C content. Although the absolute level of available P did not differ remarkably among the texture types, the availability decreased with the increase of the contents of exchangeable Al, dithionite citrate soluble Fe, and clay. The amount of C, and total and available N and P stored in soils (0-150 cm depth) varied widely depending on the texture. The finer soils stored larger amounts of these elements which were distributed more largely in the subsoils (30-150 cm) than it has been believed.