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Toward achieving uniform crop growth within a potato field, surface humus content, growth, yield and starch value were investigated in a test field whose preceding crops were carrot and soybean. Maps of surface humus content and potato growth were drawn using images obtained from an unmanned helicopter.

The results are summarized as follows:

(1) Field survey revealed that stem length (cm) SPAD value in mid-July was an effective index of nitrogen oversupply and potato yield. Values exceeding 3500 indicated nitrogen oversupply. Values less than 2500 indicated that the potato yield was less than the yield set as a goal for the Tokachi district.

(2) Estimation of surface humus content was done for 93% of the survey area and of stem length SPAD in mid-July for 68% of the survey area, by using the images obtained from an unmanned helicopter. It was possible to make maps of surface humus content and stem length SPAD. This in turn allowed the area of nitrogen oversupply and low yield to be extracted precisely from the map of stem length SPAD. It became clear that the danger of nitrogen oversupply was high in the high-humus area and the danger of low yield was high in the low-humus area.

(3) Regardless of the preceding crops, the map of surface humus content could explain 58% of stem length SPAD in the survey area. Toward achieving uniform crop growth, precise soil diagnosis based on the surface humus content map is necessary as the first step.