保全耕うんおよび慣行耕うんを施した火山灰土からの土壌および肥料成分の流出特性

抄録

The effects of conservation tillage on soil and nutrient losses were compared with those of conventional tillage in this study. Andosols sampled at Tama Hill in Tokyo were compacted in the plots, and then a slope model experiment was conducted under the simulated rainfall. Shaft tillage under weed cover (SW) was applied as a conservation tillage, and shallow rotary tillage (RSB) and deep rotary tillage (RDB) were as a conventional tillage. Additionally, no tillage under bare soil (NB) was set up as a control. Although the soils applied RSB and RDB decreased dry density, the pore structure was not sustained after the rainfall. However, the pores formed by weed roots in SW were sustained even after the rainfall, and enhanced percolation in the soil. So there was a tendency for surface runoff and the losses of soil, total nitrogen and phosphorus in SW to be lower than those in RSB, RDB and NB. In addition, the amounts of nutrient consumption by weeds in SW were remarkably lower than those by soil erosion. Total nitrogen and phosphorus losses from SW, even including the nutrient consumption by weeds, were only 1/3 and 5/9 of rotary tillage, respectively. Therefore, it was concluded that the pore structure formed by weed roots enhanced percolation and contributed to decrease soil and nutrient losses.