Energy balance and water use of cereal crops

Abstract

Measurements were made in spring barley ( Hordeum vulgare L., Custer) and winter wheat ( Triticum aestivum L., Colt) crops at Mead, NE, an east central Great Plains location. Diurnal and seasonal patterns of the energy balance components were evaluated using the Bowen ratio technique. The energy partitioning was controlled by the atmospheric evaporative demand (i.e., vapor pressure deficit, air temperature, wind speed) and by availability of soil water. Frequently, advection of sensible heat influenced energy partitioning strongly by increasing evapotranspiration (ET). Percentage of net radiation ( Rn) consumed by ET decreased progressively from 90 to 50% in both crops as they senesced. Stomatal conductance of the barley crop, which experienced mild water stress, decreased with decreasing leaf water potential below a “critical value” and with increasing vapor pressure deficit. Stomatal conductance in well-watered wheat responded to net radiation and appeared to be independent of leaf water potential and vapor pressure deficit. Water use efficiency ranged from 0 to 8.3 (g dry matter kg −1 water used) for barley and from 0 to 13.6 for wheat depending on the growth stage and the availability of soil water.