Excess nitrogen corresponding to about 2-3 times the amount required for forage plant growth had been applied continuously for many years in dairy farms at Shisui machi, Kumamoto Prefecture in Kyusyu because of the limited area of crop fields. Field experiments with reduced application of animal waster (RAAW) which contained only half the amount of requirements for corn plant growth were conducted to decrease nitrate nitrogen (NN) accumulation and restore the mineral balance in corn plants and crop field soil in 6 dairy farms. (1) The NN concentration in the corn stem decreased to less than 5 g/kg (dry matter basis) and no whole plant shoots with a NN concentration above 2 g/kg were observed after the reduction of animal waste application for 1 year. (2) The content of exchangeable potassium (EK) in the dairy farm soil decreased from 60 to 27 mg/100g after RAAW for 2 years. (3) Average dry yield of corn plants in the 4th year was 16% lower in the case of RAAW than in the case of excess utilization of animal composts, but the difference was not significant. The concentration of K was lower in RAAW, which resulted in the decrease of the K/ (Ca+Mg) equivalent ratio from 1.78 to 1.15 in the corn plants. These data suggest that RAAW can improve the feed quality by reducing the NN content and restoring the mineral balance in plant.