Model for predicting the field drying characteristics of grass conditioned by maceration (severe treatment)

In grass conservation systems, removal of moisture in the field is required to avoid effluent production during storage. When high drying rates are required these can be achieved by a macerating process that increases the specific surface area of the plants, ruptures plant cell walls and releases intracellular moisture to the surface of the plant material. Grass composition changes during growth from being predominately leaf generation to an increasing proportion of stem material and this has an effect on drying. A new model for estimating field drying characteristics was developed using data from laboratory drying experiments that measured the resistance to vapour pressure transfer for single leaves and stems. The model was based on the Penman-Monteith equation in which a canopy resistance parameter describes the rate of drying. The influence of the leaf and stem proportions, the moisture content at the time of cutting and the severity of the treatment on rates of moisture loss were simulated. Predicted initial drying rates agreed with measurements of actual, drying rates to within 2% during four field experiments. The higher the initial moisture content the faster the leaves dried. Macerated stems dried about two times faster than untreated stems, whereas macerated leaves were only 20% faster than untreated leaves. (C) 2000 Silsoe Research Institute.