The interpretation of trends from multiple yield maps

Yield data over 6 years (1993¯1998) were investigated for spatial and temporal trends from a 7-ha field growing winter wheat and oil seed rape. The data were combined into two maps, which characterised the spatial and temporal variability recorded over those years. Techniques were developed to show the maps in either the single crop form for winter wheat, or multiple crops that included the oil seed rape data. The two maps were then combined into a single classified management map, which denoted three categories, each with different characteristics that can have an impact on the way the field is managed. These categories were; high yielding and stable, low yielding and stable, and unstable. The spatial and temporal trends in the single crop were more stable than those in the multiple crops. In percentage terms, with a single crop, the proportions of these three classes were 55, 45 and 0%, respectively. For the multiple crops, the proportions were 58, 39 and 3%, respectively. The economic significance of these areas was assessed by the production of a gross margin map and further analysis showed that the categories returned 741, 691 and 644 £/ha, respectively.