Pasture Growth Analysis: An Investigation of the Relationship Between Biomass and Growth Rate.

An understanding of the dynamics of pasture growth is necessary to design economical and productive pasture management practices. Growth rate information is required as the basis for fundamental understanding and prediction of the dynamics of pasture growth. There is a wealth of data about practices aiming either to maximize growth rate or increase pasture production, however, to our knowledge growth rate has not been related to the pasture biomass present. The study of pasture growth rate can be approximated by the sigmoid Gompertz equation. This equation has four parameters which can be determined from field experimental data and also can be used to support grazing models. Therefore, the aim of this study is to understand the relationship of standing pasture biomass and growth rate of a cool-season grass in Ohio and Wisconsin. Eleven beginning dates of pasture biomass accumulation, from April to October, were fitted to Gompertz equations. The four parameters and the instantaneous growth rate were determined from the first differential of Gompertz equation for each day of evaluation across all treatments. This analysis found the relationship varied by the time of the year. The main features to respond to the amount of biomass present were the maximum growth rate and the pasture biomass values that define the limits for >90% of maximum growth rate. A pattern of the Gompertz equation parameters was found throughout the experimental period. This has a valuable application because these data can support grazing decisions such the biomass at which to start and stop grazing and allow prediction of the impact on growth rate of a specific grazing (or defoliation) regime.