Abstract
As a part of studies on forage roots and physical properties of grassland soil, the present experiment was conducted to investigate an effect of growth of grass roots on soil structure at plow layer. The soil used was KUROBOKU-soil, and experimental plants were timothy and upland rice. The results are summarized as follows ; (1) The forage roots concentrated in the layer from 0 to 10cm, though the soils were uniformly placed in the plots. (2) The percentage of new roots in forage roots was more than 40% through the experimental period. (3) The soil-hardness and solid ratio increased remarkably at 5cm depth in the forage plot and at 15cm depth in the rice plot. The former depth was due to the influence of growth of root-system and the latter depth was derived from impact such as plowing. (4) The effective soil aggregates (>1mm) were developed with the growth of root-system in both plots. However, no relation was observed between aggregates development and roots distribution. (5) The increase of effective soil-pore (1.5<pF<2.7) was recognized at 5cm depth in the forage plot. And compared with the rice plot, total soil-pore in the grass plot was less than that in the rice plot section, but effective soil-pore in the forage plot was more abundant than that in the rice plot.
