A study on clarification of nitrogen load and countermeasures in the upland distributed in the Shirasu plateau of southern Kyushu [Japan]

Andsol field is distributed in the most part of plateau consisting of Shirasu; the pyroclastic materials, with extraordinarily high water permeability in the Southern Kyushu, and upland farming and livestock raising are run advantageously there on the climate conditions of clement frequent rain, producing nitrogen as that result. The objectives of the present study are monitoring of nitrate concentration of underground water as circumstance water around the Shirasu plateau to examine the influence of nitrogen of agricultural origin on the quality of underground water and clarification of sources of nitrogen load to propose effective countermeasures. A study was executed in the Kasanohara Plateau where the plateau in the Southern Kyushu was represented, situating in the center of Osumi Peninsula of Kagoshima Prefecture. The nitrate-nitrogen concentration of underground water around the Plateau distributed between 3.3- 17.6mg/L, it is recognized that nitrate load of underground water due to leaching from the agricultural fields occurred obviously. Especially, in springs of the western region the nitrate-nitrogen concentration exceeded 10mg/L (the environmental standard value). It was estimated that the pollution of spring water in the western region by nitrate was caused by leaching and contamination of livestock wastes, and most of the nitrate load was caused by the unlined storage pond method as a pig waste management. The efficiency of nitrogen as nitrogenous fertilizer included in livestock waste composts was evaluated in contrast with the nitrogen of chemical fertilizer by cultivation examinations for several kinds of crops. It was estimated as 30-40% for the cattle dung compost, as 50-60% for the pig dung compost and as 60-70% for the chicken dung compost respectively. It was clarified a reasonable blend ratio of the pellet of livestock waste compost for every crops and combination with chemical fertilizer. Especially, in the case of continuous use of the livestock waste compost we should choose a planting system because did not let accumulate the nitrogen which remained in the soil, and we should do effective combination with chemical fertilizer.