The Influence of Mechanical Method in Grassland Establishment on Physical Condition of Subsoil

Abstract

In the present paper, we deal with the changes in physical properties of subsoil due to mechanical operations, especially, concerned with the method of plowing, as a part of the studies on the mechanical method of grassland establishment. The soil of this experiment is volcanic ash soil in Kamikita region, Aomori Prefecture. The results are summarized as follows ; 1. In case of the brush breaker plowing method, it was observed that disturbed soil layer was 70cm in the depth. In this layer, soil porosity decreased from 80% to 60%, and the coefficiet of permeability decreased to the order of 10^<-5>cm/s, that was only onetenth of the original. 2. In case of the harrowing method, disturbed soil layer was about 15cm in the depth, and the effect of this disturbance was small. The decrease in soil porosity content was only 5%, and the soil permeability showed one-half reduction. 3. As a result of slaking test, stability to water immersion of subsoil decreased to 70% by the plowing and this did not recover to the original level even after one year of the work. 4. The above results show that grassland foundation just after mechanical operation is unstable to water immersion.