Spray Losses and Partitioning of Water Under a Center Pivot Sprinkler System

Abstract

ABSTRACT CENTER pivot irrigation is extensive in the Great Plains agricultural region. The efficiency of a center pivot sprinkler system was analyzed by monitoring spray losses under various climatic conditions and by examining the partitioning of water within a corn (Zea mays L.) canopy. Average spray losses were 12% in 1980 and 16% in 1981. Spray losses were significantly correlated with vapor pressure deficit (r^ = 0.49), temperature (r,^ = 0.47) and a wind-vapor pressure deficit term (rXjy = 0.45). The unexplained variability in the data may be attributed to the difficulty of determining the exact application rate at a particular area of the field and to the interaction between climatic conditions and wind orientation relative to the sprinkler lateral. Under full canopy condition in corn, about half of the water reaching the soil surface is via stemflow with the remainder falling or dripping through to the soil surface. We found 2.7 mm of canopy storage in a full corn canopy. Net loss of plant intercepted water depends on the temperature and on the ratio of canopy (rc) and aerodynamic (ra) resistances to vapor flux, with net losses being small if rc/ra is low and temperatures are high.