Water use rate and crop factors of Italian ryegrass (Lolium multiflorumLam.) under simulated grazing conditions in a small plot experiment

摘要

No species specific irrigation norms are available for pastures in South Africa. A small plot experiment was conducted to establish irrigation norms for Italian ryegrass. Potential evapotranspiration was calculated by the Penman-Monteith formula. Crop factors were determined as the ratio of evapotranspiration to potential evapotranspiration. It was found that monthly mean evapotranspiration rates were generally lower during winter than had previously been assumed. The evapotranspiration rate also varied considerably during the harvesting cycle. Evapotranspiration rates of less than 15 mm week#x2212;1occurred frequently during the first half of the season. They increased to more than 40 mm week#x2212;1during the second half of the season. The highest values were generally measured during the last week prior to the removal of above-ground biomass. The crop factor was as variable as the evapotranspiration rate. The monthly mean crop factor increased as the season progressed except for a slight decline during midwinter. Weekly determined crop factors were generally low after harvesting. Values of 0.4 or less occurred during the first half of the season. During the latter half of the season they increased to 0.9 in the later stages of the harvesting cycles. A few values of more than 1.0 were also recorded.