Effects of crop properties, weather conditions and mechanical treatments on the wilting rate of diploid and tetraploid Italian ryegrass for silage

The relationships between rate of water loss of Italian ryegrass (Lolium multiflorum) and crop properties, weather conditions and mechanical treatments were studied on a field scale, as was the importance of the variables and their combined effects on influencing the wilting process. Eleven forage-drying experiments were performed between 1992 and 1994 on diploid and tetraploid cultivars cut at different growth stages, ranging from early elongation to flowering, under environmentally variable conditions. The rate of drying was measured until a moisture content of 1 g water g(-1) dry matter (DM) (500 g kg(-1)) was reached, or for a maximum of 2 days by calculating the rate of water loss from two consecutive hourly weights of swath portions placed on trays. Multiple regression analysis was used to correlate the drying rate (k) with crop properties and with meteorological and mechanical treatment variables. The interaction between potential evapotranspiration (ET(o)) and the moisture content of grass at cutting (M(grass)) appeared to be the most important variable, from the twenty-one tested, in influencing k. This variable shows that the same quantity of energy available for evaporation acts in different ways when the water content of the crop at cutting differs. The rate of water loss is also influenced by the M(grass) itself, surface density of the swath, tedding and the weather conditions on the first day of drying. The value of M(grass) at cutting is greatly dependent on crop maturity and ploidy. The tetraploid cultivars, with a higher initial moisture content, lost water more slowly than diploid cultivars did. Because the date of cutting cannot be delayed, owing to the decline in nutritive value, it is helpful to select for cultivars with low moisture contents at cutting, as well as applying mechanical treatment (spreading and tedding), in order to keep the wilting period as short as possible. A validated drying model can be useful for operational purposes to understand the drying process and to assess technological choices for forage drying.