Grazing and production in seasonal pastures: analysis of a simple model.
Abstract
A model is postulated to describe biomass dynamics in pastures that are grazed continuously throughout a limited growing season. It assumes that: rates of growth and intake both depend only on total green biomass (V); each dependence can be expressed by 2 linear segments; the growing season starts with a low initial biomass (Vo) and ends after a fixed time (te). The model allows for 2 effects of grazing on pasture dynamics, both through delays in the accumulation of biomass: early in the season, lengthening the periods in which biomass is subopt. for intake and growth rates; later in the season, restraining the development of biomass levels which are supraopt. for growth. The first effect is always prominent; the second one only occurs in fast-growing long-season pastures. Some of the results of the model follow. These results must be regarded as tentative; they can be expected to be valid only in those real situations where the assumptions of the model are reasonable approximations.