抄録
A field experiment was conducted to observe the effect of compacted layer destruction of soil by disk plow, mouldboard plow and subsoiler in a field of Brazilian Dark Red Latosol in Cerrado.
1. From the results of tilling depth and soil hardness distribution measured immediately after mechanical treatments, the destruction effects of compacted layer by mouldboard plow and subsoiler were larger as compared with the treatment of disk plow.
2. In the heavy disk harrow plot, as a control plot in which compacted layer is found, the tap roots of soybean bended horizontally on the upper part of compacted layer. On the other hand, the tap roots elongated more deeper in the mouldboard plow and subsoiler plots. And the tap roots elongation in the disk plow was relatively shallow. The roots elongation tendency of millet (2 nd. crop) and sorghum (3 rd. crop) cultivated with direct drilling after soybean was similar to the case of soybean roots in each mechanical treatment. The yields of stem of soybean and dry matter yields of top of millet and sorghum were small in the plots of heavy disk harrow and disk
plow.
3. The air and water permeability and chemical properties in compacted layers were excellent. On the contrary, the soil hardness of compacted layers was more than 15 kgf/cm2 at the field capacity. Accordingly, very high values of soil hardness in compacted layers were considered to be problems for root growth.
4. From the results of soil hardness distribution measured with time, the durable effect of compacted layer destruction by mould board plow and subsoiler was maintained at least one year and five months. The continuous measuring of soil hardness change is in the plan.
