THE RELATIONSHIP BETWEEN CROP YIELDS FROM AN EXPERIMENT IN SOUTHERN ENGLAND AND LONG-TERM CLIMATE VARIATIONS

This study examines the relationships between meteorological variables (average monthly maximum and minimum air temperature, total monthly precipitation) and crop yields of a long-term field experiment in southern England. The aim is to determine whether the long-periodic changes in crop yields are associated with climatic variations. This investigation uses the grain and straw yields (from 1854 to 1967) of the Broadbalk winter wheat experiment at Rothamsted, UK, which is one of the oldest agricultural field experiments in the world. In this study the main techniques used to describe the crop/weather relationships are correlation analysis and multiple regression. The results show that the long-term changes in crop yields at Rothamsted are partially related to climate variations at this site. The main influence on grain yields is precipitation. In all months there are negative correlations between grain yield and rainfall. A weak positive correlation is found between precipitation and straw yield from April to June (stem elongation) whereas in the other months the correlation coefficients remain negative. The maximum air temperature is positively correlated with the straw yield in all months except May, June and July. Generally it is easier to explain the variability of straw yields by weather variations than it is that of grain yields. On the basis of simple multiple regression models it is possible to explain 33% of the grain and 50% of the straw yield variability by precipitation and temperature variations. Long periodic changes in rainfall and temperature are reflected in estimated crop yields. The lowest grain and straw yields are observed in wet/cold as well as in wet/warm years whereas the highest grain yields are more frequent in dry or cold years and the highest straw yields in dry or warm years.