Influence on runoff of nitrate ion by compost application in a greenhouse culture with high groundwater level

The amount of nitrogen runoff under high-groundwater conditions was evaluated and its influence on environmental loading resulting from application of the cow waste compost was clarified. Environmental loading was clarified by estimating the nutrient balance of nitrogen and concentrations of nitrate ion and chlorine ion in the soil solution during the five-year test period. 1) Environmental loading of nitrogen attributed to cow waste compost became 115 g mE-2 in the standard application area and 227 g mE-2 in the heavy application area. Those results corresponded to the input of cow waste compost's original nitrogen content. 2) Chlorine ion concentrations in the soil solution, which increased according to the application amount of the compost, were 1.5 times higher in the standard application area and twice higher in the heavy application area compared to the control area. The cow waste compost original components were confirmed to have been loaded to the environment. 3) A slightly elevated value of nitrate ion concentration was indicated in the standard application area, but only an equivalent value to the comparison area was indicated in the heavy application area. Nitrate ions were inferred to have been fixed or denitrificated before reaching 60 cm underground. 4) Vertical distribution of the soil nitrogen-indicated that the first and second layers near the surface were nitrogen enriched, but the nitrogen content was lower in the third and fourth layers, where underground water rose frequently, in the heavy application area. The results described above indicate that the denitrification amount of the nitrate ion loaded to the soil increased according to heavy application of the cow waste compost because of soil reduction caused by rising underground water, which influenced the enriched organic matter. Results suggest that the nitrate nitrogen concentration in the underground water is not increased for at least five years.