Journal of Oil Palm Research Vol. 11 No. 2, December 1999, p. 72-88 KHALID, H*; ZIN, Z Z*; ANDERSON, J M**
During oil palm replanting, substantial amounts of the above-ground oil palm residues were available which contributed about 577 kg N ha-1 and 40 t C ha-1 and the root materials produced about 65 kg N ha-1 and 8 t C ha-1. These materials were the main sources of C and N which would affect the mineralization of C and N in the soil. In this study, the potential mineralizable of N, the mineralization of organic C through soil respiration and CO2evolution with different residues management practices were estimated.
The results of C mineralization study showed that the carbon fluxes due to crop residues inputs contributed about 7.7 t CO2 ha-1 yr-1 which was mineralized from the soil. However, the mineralization rate of C from the light fraction organic matter which accumulated on the top soil surface was found to be about 20 times higher than that in the soil under the organic layer. The CO2 fluxes might largely reflect microbial activity from different residue treatments.
Nitrogen mineralization due to the inputs of crop residues could significantly increase the availability of N to the young palms of which about 421 kg N ha-1 yr-1 were mineralized from the mineral soil and made available to the palms. In contrast, the N mineralization from the plot without crop residue inputs only contributed about 312 kg N ha-1 yr-1 which probably came from decomposed roots of the previous crop. Thus, the fluxes of about 109 kg N ha-1 yr-1 was transferred to the soil as a consequence of leaving crop residue about the ground during replanting of the plantation. A large amount of N was in the labile pool of the light fraction organic matter which accumulated on the top soil surface and which, when mineralized, was six to seven times higher than that in the soil under the organic layer.KEYWORDS:
* Palm Oil Research Institute of Malaysia,
P.O. Box 10620, 50720 Kuala Lumpur, Malaysia.
** Department of Biological Sciences, University of Exeter, U.K.