EVAPOTRANSPIRATION BY IRRIGATED GRASS AS RELATED TO FERTILIZER

Abstract

Efficiency of water use by a mixed sward of orchardgrass (Dactylis glomerata L.), creeping red fescue (Festuca rubra L.), and bromegrass (Bromus inermis Leyss.), fertilized with three levels each of nitrogen and phosphorus in all combinations and irrigated to promote maximum growth, was increased with increasing applied nitrogen. Yield response to nitrogen fertilizer was large and to phosphorus fertilizer was small. When total dry plant material exceeded about 4 metric tons/ha, increases of evapotranspiration with increased crop size were relatively small. The greatest daily rates of crop growth and the most efficient use of water by the crop occurred in midsummer on plots fertilized with nitrogen at 420 kg/ha. The ratios of evapotranspiration to estimated solar radiation expressed as evaporation equivalent were similar to those reported for crops in the western United States.