Short-term effects of soil water, defoliation and rangeland condition on productivity of a semi-arid rangeland in South Africa

Over a 3 year period, selected sites in three categories of rangeland - goo d, moderate and poor - were subjected to varying levels of frequency and in tensity of defoliation. Three watering regimes - normal, below-normal and a bove-normal - were applied. The effects of defoliation and levels of soil w ater were evaluated in terms of the production of above-ground phytomass an d water-use efficiency (WUE) in relation to evapo-transpiration (Et). For a ll treatments, rangeland in good condition (RC1) produced significantly mor e phytomass (p less than or equal to 0.01) and used water more efficiently (p less than or equal to 0.01) than those in moderate and poor condition (R C2 and 3). High intensity/high frequency defoliation caused a significant ( p less than or equal to 0.01) increase in phytomass production and WUE, und er conditions of high soil water availability. Generally, rangeland conditi on in interaction with the soil water content are the main determinants of optimal production and WUE. Statistically significant (p less than or equal to 0.01) linear relationships between phytomass production and Et were det ermined for all rangeland conditions and defoliation treatments. In degrade d rangeland, water is used inefficiently regardless of the quantity of wate r received. (C) 1999 Academic Press.