Abstract
The effect was studied of cutting and burning and fertilization (NK and PK) treatments on the mineral content and organic matter production of savanna grasses (Trachypogon plumosus, T. veslitus and Axonopus canescens) of Central Venezuela. Burning increased the N, P and S contents of grass leaves produced immediately after burning, but mineral concentration at the end of the growing period (186 days) was similar in both cut and burnt plot due probably to the 30 per cent higher organic matter production induced by burning. Fertilization with N + K and P + K increased the concentration of these elements in plant tissues, but at the end of the growing period the N content was reduced to that of the controls while the P content remained high. The conclusion, therefore, that was the main limiting factor for growth in the Trachypogon savannas was supported by the finding that then N + K fertilization led to higher organic matter production than P + K fertilization. Potential N losses due to volatilization through fire were 11·5 kg/ha, which represents about 0·5 per cent of the content of soil layers utilized by the grass roots.
