Studies on the water quality for irrigation, the conservation technique and the application to crop production in Tochigi [Japan] Prefecture

The author investigated the quality of irrigation water for 14 elements including nutrient salts in Tochigi Prefecture from 1996 to 1998. The water quality was acceptable in nearly all of Tochigi Prefecture. But there were a few spots with polluted water in the areas of downstream from cities in the southern and western part of Tochigi Prefecture. The nutrient salt concentration in 1996-1998 tended to be lower than that in 1986-1988, especially in T-N. The author analyzed the quality of the groundwater for irrigation at the Mibu plateau where cultivation of upland crop is the most active region in Tochigi prefecture. Our results showed that although the concentration of nitrate nitrogen in the groundwater did not exceed the environmental standard (10 mg/L), the concentration was higher than that in other areas in Tochigi prefecture. According to the results obtained from experiments using the delta sup(15)N value method and the land use, it was suggested that the chemical fertilizer greatly influenced the water quality of the groundwater. The yield of bottle gourd (Lagenaria siceraria var. hispida) and the leaching of nitrogen from the soil were compared between plots that had been treated with standard fertilizer and plots that had been treated with heavy fertilizer. The yield of bottle gourd in the heavy fertilizer-treated plots was 10% higher than that in the standard fertilizer-treated plots. From the viewpoint of cost performance, there was no economic advantage because the increase in income from the high yield was equivalent to the increased cost for fertilizer. It is suggested that the pollution of nitrogen in groundwater is caused by crop growing using heavy fertilizer. The author developed the granular fertilizer from pig wastes by mixing with calcium oxide. The alkali content was approximately 50%. The granular fertilizer had liming effect. It could be kept for a long time at the normal temperature without moisture absorption and quality changes. It was hard and could be transported and scattered by a machine. A large amount of ammonia gas generated by the reaction of pig wastes with calcium oxide could be absorbed by palm shell that contained phosphoric acid liquid. The author developed the granular fertilizer from sewage sludge by the same method of pig wastes. The automatic manufacturing device was developed in cooperation with the private machinery manufacturer, obtaining seven patents. The author developed the pellet fertilizer from livestock waste by adding chemical fertilizer and clarified the properties and its effect on the growth of leafy vegetables and rice. The chemical component of the fertilizer was adjusted to the desirable value by analyzing the chemical components of the raw livestock waste and adding the necessary amount of chemical elements. The fertilizer was uniform in quality and the contents of nitrogen, phosphoric acid and potassium were approximately 5%, 5% and 5%, respectively. When sealed in a resinous bag, it could be stored for a long time without quality change. During incubation at 30degC, the livestock waste fertilizer maintained almost the same nitrogen mineralization rate as the commercial organic pellet fertilizer. The yield of komatsuna and spinach cultivated by applying the livestock waste fertilizer was the same as that cultivated by applying the organic fertilizer in the market. The yield and the quality of rice by applying the livestock waste fertilizer was the same as that cultivated by applying the general fertilizer. The author evaluated the water purification ability of the paddy fields by the water quality observation data and the water balance data. Only the element that was purified in the water of paddy fields was N. Casup(2+), Mgsup(2+), Nasup(+), Clsup(-) and SO4sup(2-) were estimated to run out of paddy fields because the amount of secondary ingredients of fertilizers and various organic materials such as composts which were brought in the field was larger than the absorbed amount by rice plants. It was estimated that the nitrogen of 71 kg/ha disappeared in rice field region where polluted water was used. It was mainly caused by denitrification of the paddy soil.