Yield of sugar beet in relation to weather and nutrients

Data on sugar beet yields from a long-term experiment (1965-1993) at IACR Broom's Barn are used, in conjunction with long-term weather data, to assess the degree to which weather affects yield and how this effect is modified by nutrient availability. Mean temperatures and rainfall during July and August were strongly correlated with sugar beet yields, as well as mean temperature during April and the length of time between sowing and harvest. The data from July and August were entered into a factor analysis to generate two factors describing how hot and dry weather conditions are during July and August. These two factors, as well as April temperature and the length of the growing season, were entered into a multiple regression. The regressions revealed strong effects of the principal axis factors on sugar beet yields across treatments, as well as strong effects of the length of the growing season, but weaker effects of April temperatures. The strength of response to weather was dependent on the nutrient regime, and was, in particular, greater with increased application of nitrogen. There was, however, no effect of nutrient regime on the strength of response of yield to the length of the growing season. These results indicate that weather-induced year-to-year variability in sugar beet yields in unirrigated crops is primarily determined by conditions in July and August as well as the length of time between sowing and harvest, and imply that drought limits yields in well-fertilised crops. The practical implications of these results are that the risk of yield losses due to drought may be minimised by maximising the length of growing season, and that there is the potential for developing simple measures to forecast yields through monitoring of rainfall. (C) 1999 Elsevier Science B.V. All rights reserved.