The effect of defoliation and moisture stress on the productivity of Themeda triandra Forsk. under controlled conditions.

Abstract

Range managers in semi-arid and arid regions in the Republic of South Africa must take into consideration the incidence of droughts and the detrimental effect of incorrect grazing practices during drought periods. Trials were conducted with Themeda triandra, during three phenological phases, in pots to determine the effect of severe, moderate and no defoliation, before and during periods of moisture stress, on the productivity of the plants. Themeda triandra plants in the vegetative and reproductive stage were affected the most severely as reflected by dry matter production, root mass and total available carbohydrate (TAC) content. When Themeda triandra in any phenological phase was subjected to relative short periods (up to three weeks) of moisture stress there was a significant increase in root mass. The TAC content of the roots and stubble increased during periods of moisture stress but decreased significantly after the plants had been re-watered. Themeda triandra plants in three phenological phases showed marked differences in respect to water use efficiency and dry matter production under the different treatments. Lenient defoliation before and during periods of moisture stress seems to be more beneficial than severe or no defoliation.

Keywords: afrikaans; carbohydrate; defoliation; drought; dry matter production; grazing; moisture stress; productivity; root mass; south africa; stress; themeda triandra; water use; water use efficiency