Evaluation of Soil Physical Properties Using Cylinder Infiltrometer Method in Soybean Fields Converted from Clayey Paddy Fields of Hokkaido

Abstract

A soil physicochemical survey was conducted on soybean fields converted from clayey paddy fields in the western part of Hokkaido. A cylinder infiltrometer method was used as a simple method for the evaluation of soil physics. The soil chemistry of the surveyed fields was within the range of the soil diagnosis criterion, but there was a tendency for many of the fields to show poor soil physics below the shallow topsoil. When the basic intake rate (I_b) measured in the surveyed fields was less than 100 mm･h^-1, grain yield per plant was affected and the grain yield per square meter was less than 300 g･m^-2, although there was no relationship to planting density. Analyzing the relationship between I_b and soil physical properties using quantification theory type II, it was found that a soil structure that was underdeveloped and had few cracks and pores reduced the I_b to less than 100 mm･h^-1, and the yield of soybeans was consequently lowered. On the basis of these results, we concluded that the cylinder infiltrometer method that reflects the soil status in terms of the presence cracks and pores can be applied for evaluation of soil physical properties in fields under soybean cultivation that were converted from clayey paddy fields, with an I_b of 100 mm･h^-1 or more indicating an improvement in the index value of the soil physical properties.