Study on measures to prevent fine red soil particles from runoff using chemical fertilizers

这项研究是在科学研究补助金的资助下完成的。很明显，化肥分散了土壤颗粒，防止了土壤颗粒沉降。由于化肥使土壤颗粒变细，加速了农田土壤的径流，防止了沉淀池的沉淀。其结果是，土壤细颗粒从农田和沉淀池流出，然后海岸被红壤污染。在化肥对土壤的分散试验中，分别在纯水和加有化肥的水中对土壤颗粒进行筛分，比较了两种条件下土壤防水团聚体的粒径分布，结果表明，加入化肥后，小于0.25mm的细颗粒增多。在对国上町土进行的水中添加化肥的试验中，确认了少量添加化肥时土壤颗粒分散，大量添加化肥时土壤颗粒凝聚的现象，认为这是由于磷酸的特异性吸附使电荷由正变为负，负电荷增加，使细小的土壤颗粒分散。然而，通过添加更多的磷酸，磷酸的比吸收饱和，并且负电荷停止增加，并且正电荷通过添加更多的磷酸而增加，并且负电荷被正电荷中和。这个过程被认为是凝聚力的原因。

This study was done with the Grant-in-Aid for Scientific Research.It became clear that chemical fertilizers dispersed up soil particles and prevented soil particles from settling. Because chemical fertilizers make soil particles fine, soil runoff from farmlands is accelerated, and sedimentation in settling ponds is prevented. As a result, fine soil particles flow out from farmlands and settling ponds, and then seacoast is polluted by red soil. In the experiment of the dispersion of soil by chemical fertilizers, soil particles were sifted in the pure water and the water with chemical fertilizers, and the size distributions of the waterproof aggregation of two conditions were compared.As a result, it was recognized that fine particles smaller than 0.25mm increased by adding chemical fertilizers. In the experiment that chemical fertilizer was added to water with Kunigami maji soil, it was confirmed that soil particles were dispersed by adding little chemical fertilizers and cohered by adding much.The reason of this phenomenon was supposed that electric charges changed from positive to negative by the specific absorption of the phosphoric acid, and negative electric charges increased, and fine soil particles were dispersed. However, by adding more phosphoric acid, the specific absorption of the phosphoric acid was saturated, and negative electric charges stopped to increase, and positive electric charges increased by adding more phosphoric acid, and negative charges neutralized with positive charges. This process is supposed the reason of the cohesion.