EFFECTS OF CROP PROPERTIES, WEATHER CONDITIONS AND MECHANICAL TREATMENTS ON THE WILTING RATE OF DIPLOID AND TETRAPLOID ITALIAN RYEGRASS FORSILAGE

The relationships between rate of water loss of Italian ryegrass (Loli um multiflorum) and crop properties, weather conditions and mechanical treatments were studied on a field scale, as was the importance of th e variables and their combined effects on influencing the wilting proc ess. Eleven forage-drying experiments were performed between 1992 and 1994 on diploid and tetraploid cultivars cut at different growth stage s, ranging from early elongation to flowering, under environmentally v ariable conditions. The rate of drying was measured until a moisture c ontent 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. Mult iple regression analysis was used to correlate the drying rate (k) wit h crop properties and with meteorological and mechanical treatment var iables. The interaction between potential evapotranspiration (ETo) 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 e vaporation acts in different ways when the water content of the crop a t cutting differs. The rate of water loss is also influenced by the M- grass itself, surface density of the swath, tedding and the weather co nditions on the first day of drying. The value of M-grass at cutting i s greatly dependent on crop maturity and ploidy. The tetraploid cultiv ars, with a higher initial moisture content, lost water more slowly th an diploid cultivars did. Because the date of cutting cannot be delaye d, owing to the decline in nutritive value, it is helpful to select fo r cultivars with low moisture contents at cutting, as well as applying mechanical treatment (spreading and tedding), in order to keep the wi lting period as short as possible. A validated drying model can be use ful for operational purposes to understand the drying process and to a ssess technological choices for forage drying.