The objective of this study was to evaluate the distribution of soil strength (measured as cone index, CI) along a 600 m transect and to determine the soil loosening depth necessary to eliminate zones with soil strengths exceeding a threshold value down to a depth of 0.6 m. The transect was located at a site in a glacial drift area which was characterised by sandy deposits overlying boulder clay. A tractor-mounted multi-penetrometer array consisting of four hydraulically driven single vertical penetrometers was used to determine CI at 1-m sampling intervals as a measure of penetration resistance. The spatial fluctuation of the CI readings in general and that of repeatedly averaged readings along the transect was examined. Furthermore, the relationships between the penetration resistance of several soil layers and the relationships between the CI of single penetrometers were identified. Averaged CI values over 5-m intervals were used to determine the depth of soil loosening required. By using various data sub-sets based on the averaged data of the four array mounted penetrometers and simulating several different sampling intervals, treatment intervals and threshold values of soil strength, a sampling interval of about 10 m proved to be sufficiently accurate to determine the loosening depth required.
Yield maps derived from yield mapping systems are often erroneous not only due to limitations in measuring the yield precisely but due to insufficient consideration of the requirements of yield mapping systems in practice as well. Aerial images of cultivated crop fields at an advanced growth stage frequently provide a spatial pattern similar to that of yield maps. Therefore, the possibility of generating a yield map using aerial images and measured yield data of a few tracks was examined for a period of 2 years in two fields grown with cereals. Yield zones based on Visible Atmospherically Resistant Index (VARI) values were compared with yield zones based on measured yield data of the whole field. About half of the grid cells of a field were allocated to the same yield zones irrespective of the mode of yield determination. Using the Kruskal-Wallis test, the data sub-sets of measured yield within the yield zones based on the VARI values differed significantly for all tested yield zones. As a result, the approach was successful in the case of these experimental sites.
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