Intra-field yield variation over crops and years

Data and yield maps were obtained from farmers using their own combine harvester equipped with commercial systems for yield measurements and satellite positioning. Three quarters of the datasets collected were abandoned due to being incomplete or problems occurring when overlaying maps from different years. Intra-field yield variation was investigated in the remaining 82 fields. Some fields had data present for 4 years. The predominant crops were winter wheat and winter barley. The coefficient of variation (cv) ranged from 0.05 to 0.22, which was comparable to the residual cv usually found in agricultural experiments. In spring and winter rape the average cv was 0.15, cereals varied from 0.05 to 0.22. The distribution of yields within fields was generally non-normal; it was negatively skewed (left tailed) and broader than a normal distribution. Although the highest yielding crops and fields had the lowest intra-field variation, the distributions of yield were mostly negatively skewed. Regression analyses of intra-field yield pattern between years gave R2 values from 0 to 0.81, with an average of 0.27. Similar crops and crops with small average yield differences gave the highest R2 values, even when they were separated by more than one year in time. Prediction of intra-field variation, trend maps of temporal stability, and maps of classified management, could therefore be improved by developing them for individual crops based on the most appropriate previous crops. It appears unlikely that trend maps will account for much more than 1/3 of the annual intra-field variation on average. The possibilities for developing maps of classified management based on similar quality yield maps as obtained from farmers in the present investigation, appears limited because of the high frequency of erroneous data sets, systematic errors in the recorded data and their restricted yield predictive ability.