Factors affecting the seasonal variation of veld quality in South Africa.

Abstract

This project was initiated to investigate the factors affecting the seasonal variation of veld quality in South Africa, with specific objectives as follows: (1) to establish what factors might play a role in seasonal variation of plant quality in South African grassveld; {2) to provide a more objective definition of the terms sweetveld and sourveld than already exists; (3) to determine an objective and quantitative method of measuring or indexing the degree of sweetness or sourness of a representative species of both sweetveld and sourveld using Themeda triandra as the reference species and (4) to establish which factors, if any, may be manipulated to improve veld quality. The results indicate that cellulase dry matter digestibility, neutral detergent fibre, nitrogen status and phosphorus levels were the plant factors most important in indicating veld quality. Climate and soil fertility were found to have no consistent relationship with veld quality. Thus any definition of sweetveld and sourveld will have to be based on the winter quality of veld and not on the climate or soil fertility. The winter quality of veld appears to be a function of the seasonal quality patterns of all species present and not only a reflection of the winter quality of '.L_ triandra. As the seasonal quality patterns are likely to vary between species, management will influence the degree of sourness in the long term by influencing species composition and in the short term by affecting the ontogeny of the plants present i.e. the amount of preferred material left on palatable and unpalatable species available for winter grazing. The seasonal quality pattern and inherent winter quality of '.L_ triandra has been shown to vary considerably from area to area. As each species is expected to show unique quality patterns, the sweetveld/sourveld situation becomes extremely complex. There are no obvious factors (except management) that can be manipulated to improve the winter quality of veld.