Simulation of senescence and disappearance rates in irrigated and dryland pastures

Abstract

Previous experiments with a sheep farm grazing model suggested a weakness in assumptions concerning pasture senescence and disappearance rates which was influencing the quantity and more importantly quality of pasture on offer and hence animal performance. Data from the Winchmore Research Station describing pasture masses and the amount of dead material in irrigated swards over several years have been used to derive joint estimates of growth and senescence rates and produced patterns similar to the few data available in the literature. Subjective estimates were made of likely differences in senescence between dryland and irrigated conditions and the model used to simulate the implications of these assumptions. Results demonstrate the sensitivity of animal performance to assumptions about the senescence and disappearance rates of pasture, particularly in the dryland situation where previously unrealistically high levels of performance were reduced closer to expected levels. This reinforces the desirability of collecting data on dead material in trials involving pasture measurements. Pasture production, percentage harvested and animal performance estimates from the model are presented. Keywords: Lolium perenne, pasture disappearance, pasture senescence, sheep grazing, simulation model, Trifolium repens