Effects of No-tillage Practice on Nitrate Leaching in Sugar Cane Fields in Sub-tropic Area

Abstract

No-tillage cropping (NT) is considered as a better onsite counter measure to reduce runoff and soil loss than the soil conservation techniques in sub-tropic area in Japan. In this paper chemical and physical soil analysis and field survey have been conducted to clarify effects of NT on retention and leaching of soil nutrients at sugarcane field. Sugar cane fields under conventional tillage (CT) and the NT were the studied sites in Ishigaki, Japan. Shimajiri mahji soil, having clay content of more than 50%, covers the study site. An observation ditch of 100 cm in width and 70 cm deep was prepared at the boundary of the CT and NT fields. Soil samples for chemical and physical analysis were taken and PVC cores containing ion exchange resins to trap leaching ions were inserted at both side wall of the ditch. Also, observation of sugar cane root distribution was conducted. After the survey, the observation ditch was filled up by the original soil. The CT had shallow and sparse root distribution while the NT showed denser and deeper root distribution. It corresponded to higher saturated hydraulic conductivity of the NT soil. At the same time the NT showed lower dry bulk density and penetration resistance at the layer of 15-25 cm where the NT had more roots than the CT. The NT had greater nutrient flux at 0-20 cm deep layer, however it rapidly decreased along the depth and reached the similar rate to the CT at 40 cm deep layer. Much of the nutrients in the NT could be soaked up by sugar cane roots. Development of roots may reduce the negative effects of the NT that may enhance leaching of nutrients by bio-macro pores.