Evaluation of soil physical properties in agricultural fields using satellite images and topographic information II. Poor drainage

<p>This study investigated the relationship between satellite images, topography, and soil drainage in agricultural fields in the Tokachi district of Hokkaido, Japan, to identify areas of poor drainage. The normalized difference vegetation index (NDVI) of winter wheat was found to be lower during the young panicle formation period but increased before harvesting in areas with poor drainage. These areas were characterized by a shallower appearance of the upper boundary of redoximorphic or gleyic features, a shallower groundwater level, and lower saturated hydraulic conductivity compared to the control area. Poor drainage in these areas likely resulted in delayed initial wheat growth but pronounced later growth due to extensive nitrogen and water uptake from subsoils before harvest, or in the death of wheat and subsequent weed growth due to water logging caused by heavy rain. Significant positive correlations were observed between elevation and NDVI in the early growth stage in each field (P<0.001), suggesting that water accumulation at relatively low elevations could be another cause of poor drainage. Time-series analysis of NDVI under different meteorological conditions revealed that the delay of NDVI in poorly drained areas was not observed in years of low precipitation. In conclusion, areas of lower elevation, lower NDVI in the early growth stage, and higher NDVI before harvesting likely indicate poor soil drainage, provided the management history is consistent within the agricultural fields.</p>