Abstract
Soil crusting is one of the major problems affecting the emergence of soybean seedlings in converted paddy fields in some regions of Japan. To identify the converted paddy fields in which soybean emergence is at risk from soil crusting, we collected twenty-seven samples of surface soils from paddy fields across Japan. Relationship among physical and chemical properties, clay mineralogy and surface crusting under simulated rainfall were studied. In terms of morphology, most of the soil samples showed crust after exposure to a rainfall of 37 mm/h. With regard to the relationship between crust properties and soil characteristics, some correlations were found between the decrease in infiltration and the hardness and area of the cracks when crust dries. The infiltration rates were correlated with the mean weight diameter of aggregates. The hardness indicated a rather obscure correlation between the silt contents and acid-oxalate-extractable aluminum (an indicator of Andie properties). The cracked areas were clearly correlated with the sand contents. With regard to clay mineralogy, in the soil samples which showed no or trace peak for kaolinite and vermiculite and a clear peak for smectite, hardness did not increase after drying.
