Abstract
AbstractThe fluxes of latent heat and CO2 above an irrigated sugar beet (Beta vulgaris) field in the North Platte Valley of Nebraska were calculated by means of the energy balance. The advection of sensible heat to the field was large only when strong dry winds predominated or when the field acted as a leading edge of the irrigated river valley.Little evidence was found of midday depression in sugar beet photosynthetic rate. Contrary to reported aerodynamic evaluations of CO2 flux in the field, the energy balance calculations do not reveal a relationship between wind speed and CO2 flux, except for a negative correlation during a dry windy period. This decrease was attributed to increased stomatal resistance.The crop appeared to be light‐saturated at 0.8 cal cm‐2 min‐l short wave radiation. When CO2 flux is corrected for soil CO2 emission and plant respiration, agreement with plant sampling measurements of dry matter increase is good. Water use ranged from 171 g per g dry matter fixed on a cloudy day to an average of 365 g per g dry matter fixed on clear days. Since the sugar beet crop is saturated at less than full sunlight, water use is greater than is necessary for the production obtained.
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