抄録
Potato starch production in Japan is exclusively limited to Hokkaido district, where 30 starch factories produce 250, 000 tons of starch a year. Up to the present, waste water (WW), except flume water, is mainly applied to arable land or treated with long term airation. In this report, agricultural use and some effects of WW are reviewed. 1. The irrigation of WW has been practiced to grass land from 1969. The spray irrigation of WW deepened the green color of grasses and improved the growth and yield of orchard grass and timothy in the following spring. However, a large quantity of irrigation caused a reduction in the population of red clover in the mixture of grasses, or orchard grass in the mixture of ladino clover. The grasses fell down after heading time due to their thick growth, and were high in water content, giving rise to the difficulties in making hay. In such case, T-N, NO3-N, P and K contents of grasses were high, while Ca and Mg contents were low. A proper quantity of spray irrigation of WW, containing about 400 ppm of N and 800 ppm of K2O, was concluded to be 30 mm to mixed grassland and 60 mm to gramineous grassland a year, respectively. 2. In an optimal amount of WW, the ratio of removal to effluence was about 9:1 in N or K, and the differences between plots of fertilizers or WW were very little. When a large amount of WW was applied, the effluence of N and Ca increased temporarily. The K accumulated markedly in the soil. But, the growth and yield of the upland crops were improved. The measurement of three-element in the plots applied with WW suggested the disuse of K fertilizer, and reduction of N and P fertilizers. The amount of WW applied should be decided first by the optimal amount of K for each crop and then, N and P should be supplemented as fertilizer in consideration of the application standard of fertilizers and their utilization efficiencies of WW. The application of WW with wheat straw are considered to bring about synergistic effects, but that with beet-top (leaf and crown root) may evoke the surplus of fertilizer. 3. The WW transportation is carried out by a pipeline-sprinkler or a motor-sprinkler. The former is effective to treat a large amount of dilute WW, but it is inadequate for its application to beet field after harvest due to excess nutrients or short period before winter. Therefore, the pipeline-sprinkling method needs to cover a large area and costs a great deal. The latter is effective for the application of only fruit water to wheat field or potato field after early harvest. It makes possible to use widely, but needs the airation system for this dilute WW.
