Abstract
The effect of organic material and silicon on Pangola grass growth and phosphorus contents in a soil from Los Diamantes, Costa Rica was studied in a glasshouse experiment. There was an immediate but temporary beneficial effect on plant growth of silicon and plant residues added to the soil. Calcium silicate, rice hull and Stylosanthes humilis increased forage yields, but these increases were significantly higher than the control only at the first harvest. Forage phosphorus concentrations were increased by calcium silicate, rice hull, and S. humilis treatments. The higher forage phosphorus concentrations from these treatments may have been due to the increased availability of soil phosphorus or in the case of plant residues, to increased available phosphorus from their decomposition. Large amounts of soluble sugar added to the soil reduced forage yieIds markedly, possibly because of nitrogen and phosphorus inmmobilization. Incorporation of rice hulls, where they are abundant, into tropical soils deficient in available phosphorus, probably is a desirable practice, particularly for small, intensively managed plantings.
