The effect of defoliation during wilting on the production of Themeda triandra and Eragrostis lehmanniana in semi‐arid grassland

Abstract

The effect of defoliation during wilting on the production of Themeda triandra and Eragrostis lehmanniana was studied over four years (1977 to 1980). Defoliation whilst the plants were at temporary wilting point in the early growing season (before 1 January) decreased production from both species in the subsequent season (P≤0.01). Defoliation over the last half of the growing season, during wilting, had little effect on growth in the following season (P≤0.05). The effect of a defoliation treatment on production was not necessarily neutralised after one season's rest. Themeda triandra produced more (P≤0.01) than E. lehmanniana for each defoliation. The seasonal soil‐water extraction pattern in the soil profile was also determined. As the season progressed, plants showed visible signs of wilting at lower soil‐water content than earlier in the season. Most water extraction over the season takes place to a soil depth of 600 mm.