Abstract
Experiments were performed to investigate the relation between plant growth and soil structure. Several forms of soil structure were prepared by mixing the coarse aggregates with ground soil. The coarse aggregates were gotten by sieving the air-dry diluvial volcanic ash soil and ground soil was gotten by grinding the coarse aggregates until it passed through a 0.25mm screen. I. Seed germination of wheat as affected by soil structure. Three forms of aggregated soils were filled in specially deviced Petri dishes by placing the wheat seed in the soil. These Petri dishes were kept at constant temperature (24∼25°C) in closed container. Poor aggregation caused limitation of emergence at both high and low soil moisture meanwhile emergence was taken place at medium soil water content. It was said that the poorer the granulation in soil, the narrower the suitable soil moisture range for seed emergence. The factors which limited the emergence might be the reductive condition at higher soil moisture and crusting of soil at lower moisture. II. Relation between the growth of wheat plant at early growing stages and soil structure. Wheat plants were grown in greenhouse pots filled with 700g air-dry soils prepared to have each of the 4 forms of soil structure. Soil moisture were kept at 4 grades, supplying the water from the bottom of pot through sand layers of various thickness. A coarsly aggregated soil brought much better plant growth especially in root than did the less aggregated soil. As a possible cause of the reduced growth in the unaggregated soil, insufficient supply of oxygen is suggested and it might suppressed the ability of roots to absorb nutrients.
