Studies on the Growth of Soybean Plant in Different Environments Attended by Mechanized Cultivation : V. Growth of soybean plant in relation to soil compaction and depth of tilth

In order to make clear favorable soil conditions to growth of soybean plant (Tokachi-nagaha), a soil compaction expriment was conducted on the volcanic ash soil fields in 1968. Non-compaction, moderate-compaction and severe-compaction with 20 cm and 30 cm in depth of tilth were produced by the different driving times of the wheels of tractor. Results obtained are as follows: The ratios of solid and water to soil in volume were greater in the compacted plots than the non-compacted plot. However, the air ratio was smaller in the compacted plots. The dry matter weight and total nitrogen content of the plants, the length and thickness of the stems, a number of pods, the weight of 100 seeds and the grain yield became in the order, severe-compaction≒moderate-compaction > non-compaction and 20 cm > 30 cm in depth of tilth. Therefore, there were positive correlations between the yield (315∼339 kg per 10 a) and the solid ratio (17∼26 v%) or the water ratio (45∼59 v%), and a negative correlation between the yield and the air ratio (16∼38 v%).