PROBLEM TO BE SOLVED: To intuitively and clearly present highly accurate determination of repeated cropping failure.SOLUTION: Wheat and barleys are cropped in a field f1 on the whole in the fiscal year 2007, and the cropped area where wheat and barley are cropped is set as fb. Assuming that the same cropping articles as in the fiscal year 2007 are cropped on the same area in the fiscal year 2008 since the fiscal year 2008 is a future year, the area is set as the cropped area fa of the fiscal year 2008, and an overlapping area fab between the cropped areas fa and fb is obtained. Further an overlapping area fabc between the overlapping area fac and a cropped area fc of wheat and barley of the fiscal year 2006 is obtained. Then, an overlapping area fabch between the overlapping area fabc and a cropped area fh of wheat and barley of the fiscal year 2005 is obtained. Since the overlapping area fabch is present, it is found that wheat and barley are repeatedly cropped within the same area for 4 consecutive years. Since wheat and barley are repeatedly cropped in the overlapping area fabch for 4 consecutive years and the period exceeds repeated cropping limited years (3 years), it is determined that repeated cropping failure is present.
