畦表面硬化法による硝酸態窒素溶脱制御技術

抄録

The sweet potato is very important crop in the South-West warm region of Japan. Land for sweet potato should be plowed 20 to 25cm deep. If it was operated for deep tillage, a potential pollution hazard was increasing. Our objective in this study was to solve this problem and to establish the technique reducing NO₃-N pollution.
We have attempted to decrease water infiltiration by tillage methods.
We proposed some kinds of tillage systems. New methods of tillage systems included hammering the surface of ridge, the combined treatment (compacted soil layer and hammering soil surface) and conventionally cultivated plot. The method of hammering the surface of ridge tended to show suitable soil water storages than other two treatments.
This newly developed tillage system was found to be more effective in controling infiltration in sweet potato production during growing season, especially as rainy season.
It was obvious that NO₃-N in conventional plot had significantly greater concentration near the soil layer (60cm) in comparison with hammering plot. This might suggest that NO₃-N did not move and stayed in treatment plots. It was found that treatment by hammering the surface of ridge was lower infiltration from surface to subsoil than conventional plot. In conclusion, it was found that the new methods of tillage system contributed to reduce Nitrate-Nitrogen leaching.