Systems analysis of the effect of application methods on the entry of sulphur into pastures grazed by sheep.
Quantitative estimates of the effects of different methods of S application on the entry of 35S into the grazed pasture system were made on an analogue computer. A model of a closed recycling system was used with least-squares methods to derive estimates of parameters associated with S entry via soil and plants. Model-generated behaviour was compared with observations on the specific radioactivity of wool following a single application of 35S to pasture in solid or liquid form with high and low levels of carrier sulphate. The results showed that a model based on a simple direct entry of S into the soil and plant was capable of fitting the experimental data for all methods of S application. However, the rate constants for the entry of S into soil and plant were affected by the form of S and the method of application used.