The Broom's Barn sugar beet growth model and its adaptation to soils with varied available water content

The important environmental variables that determine sugar beet growth and yield are: temperature, radiation, rainfall, potential evapotranspiration and soil available water capacity (AWC). It is important to understand the integrated effects of these variables on the production of crop dry matter and sugar yield if reliable mathematical models are required to accurately predict sugar beet growth and yield between years and across different soil conditions. The original Broom's Barn sugar beet growth model is process-based, weather-driven and uses a daily time-step simulation. It was developed from observations on beet crops grown at Broom's Barn to take into account the integrated effects of these variables, assuming that the crop has a plant population density of >= 75,000/ha, is supplied adequately with nutrients and is free of weeds, pests and diseases. Soil at Broom's Barn is generally sandy loam and has AWC of about 14%. Initial testing of the model against sequential harvest data from commercial fields at different sites in the UK and Germany showed that the original model simulated total dry matter and sugar yields with good agreement to the field observations from soils which had AWC < 18%. However, three of the original parameters in the model had to be adjusted to accurately simulate the total dry matter and sugar yields with the field observations from soils which had AWC > 18%. The three parameters are: the rate of foliage cover decay - mu(min0), the rate of decay in intercepted radiation conversion efficiency - gamma and the sugar partitioning coefficient - K. The choice of these three parameters was based on the following observations made where water is plentiful: crop foliage cover declines at a slower rate after it reaches a maximum value; crop canopy intercepted radiation use efficiency declines at a slower rate late in the growing season as less of the canopy is composed of old leaves; the proportion of total dry matter apportioned to sugar is reduced. (c) 2004 Elsevier B.V. All rights reserved.