Dependence of sugar beet yield on light interception and evapotranspiration

This paper presents an analysis of the growth of sugar beet crops in the UK between 1980 and 1991. The objective was to account for considerable variation in yield, in response to the weather and to irrigation, using simple relationships between yield and foliage cover, irradiance, vapour pressure deficit (D) and evapotranspiration (E-T). The analysis considers an adaptation of the model of Doorenbos and Kassan [Doorenbos, J., Kassan, A.H., 1979. Yield response to water. FAO Irrigation and Drainage Paper 33, FAO/UN, Pome.] in which yield could be expressed in terms of both intercepted radiation (I) and E-T. The relative importance of either depends on the parameter k(y). Average growth rates of rain-fed and irrigated crops were 1.44 and 1.52 g MJ(-1) (epsilon), with respect to I alone, and 6.49 and 5.87 g kg(-1) (q) with respect to E-T alone, but there was significant year to year variation. In rain-fed crops, epsilon was inversely correlated with average solar radiation and in irrigated crops, q was inversely correlated with D, but the erected constancy of qD was not found. Instead, variation in yields could be better accounted for by relating yield to both I and E-T. Further improvements were possible by allowing crop growth rates to decay during the season, particularly with respect to I, when a common initial epsilon (1.76 g MJ(-1)) could be fitted that declined faster in rain-fed crops. The balancing parameter, k(y), was estimated at 0.62, the amount of yield loss per unit of E-T loss. These analyses provide a basis for simple yield forecasting models which rely on few meteorological variables and have only few easily estimated parameters. (C) 1998 Elsevier Science B.V.