A mathematical model for assessing the influence of stocking rate on the incidence of droughts and for estimating the optimal stocking rates.

Abstract

Reports the results of a study conducted to compare simulated veld production, using the Putu eleven simulation model, with veld production data; The Putu 11 simulation model was used to simulate veld production for each of 47 years, using weather input data and soil properties of a site at Glen. Grassland drought was defined as that condition encountered when 100kg/ha or less standing dry matter was simulated. Model simulations of monthly DM production at five selected stocking rates were used for determining the dates of occurrence and duration of the droughts. Simulated drought duration was found to be linearly related to stocking rate. Theoretically, no droughts were identified at stocking rates less than 6,25 ha/LSU. A simple economic analysis of the results indicated that the gross profits were optimised at a rate of 5,78 ha/LSU. The use of mathematical models for drought analysing and classification was successfully demonstrated.

Keywords: drought; drought indices; Droughts; Dry matter; glen; grassland; mathematical model; Mathematical models; Modelling; models; Optimal stocking rates; palmer index; production; Putu eleven simulation model; putu ii; simulation model; Soil properties; south africa; Stocking rates; Veld production

Journal of the Grassland Society of Southern Africa.