The possibility of introducing variable-rate nitrogen application in uplands of andosol areas as evaluated by surface soil and crop growth attributes estimated from satellite images

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  • 衛星画像から推定した表層土壌・作物生育に基づく黒ボク土畑作地帯における可変施肥導入の可能性
  • エイセイ ガゾウ カラ スイテイ シタ ヒョウソウ ドジョウ ・ サクモツ セイイク ニ モトズク クロ ボクド ハタサク チタイ ニ オケル カヘン セヒ ドウニュウ ノ カノウセイ

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<p>Variable-rate nitrogen application (VNA) based on nitrogen fertility has been introduced to upland fields in Hokkaido. This technique has been considered effective in fields where nitrogen fertility positively correlates with the variation in crop growth estimated from remote sensing, such as satellite images. This study estimated the surface soil humus contents (SSHCs) as an index of nitrogen fertility and aboveground growth of sugar beet and potato from satellite images in 123 fields in andosol areas of Tokachi region, Hokkaido. Based on the relationship between the above-mentioned soil and crop data, we investigated the number of effective VNA fields. Two satellite images were used for the analysis, one in April 2016 when the surface soil was visible and another in July 2016 (a year of heavy rain) when the crop grew abundantly. From the image in April, we found the highest coefficient of determination (R2=0.71) for the red wavelength in the correlation between image data and the measured value of SSHCs. Therefore, the SSHCs in the surveyed fields were estimated using the regression equation. Sugar beet and potato growth were evaluated by the normalized difference vegetation index (NDVI) of image data in July. The estimated SSHCs and NDVI were resampled by a 10 m grid, and then their relationship for each field was evaluated by linear regression. Resultantly, SSHCs were positively correlated with NDVI at a 1％ level in 20 fields (34.5％) for sugar beet and 31 fields (47.7％) for potato. However, those fields with high SSHCs, which have a negative correlation could have been affected by poor drainage due to heavy rainfall or low pH. In conclusion, those fields with a positive correlation between SSHCs and NDVI in the year of heavy rainfall are effective for VNA introduction in the study area.</p>

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