Environmental effect of turf-soil system disposing nitrogen in biogas fertilizers

In order to study on the effect of biogas fertilizer application on nitrogen of groundwater in turf-soil system, under the climate condition of Beijing, contrast test was made with a soil column test device of subsurface infiltration system. Below 1 m soil depth, the concentration of NH4+-N, NO3--N and total nitrogen in the turf-soil leachate were measured under the five conditions and effect of different biogas application on them was analyzed. The five conditions were that the annual application rate of nitrogen was 20, 60, 100, 140 g/(m2·a) in each biogas fertilizers and it was 20 g/m2 in the chemical fertilizer with above device. The results showed that the concentration of NH4+-N, NO3--N, total nitrogen in the soil leachate increased with rising of nitrogen dosage in biogas fertilizers. When nitrogen application was 20 g/m2 annually, the concentration of NH4+-N, NO3--N and total nitrogen in the soil leachate which was applied with chemical fertilizer was higher than that which was applied with biogas fertilizer. Ammonia nitrogen removal rates of all treatments were higher than 99.8% and total nitrogen removal rates of all treatments were 86.7%-95.6%. While nitrogen application of biogas fertilizer was 60 g/(m2·a), the highest total nitrogen removal rate was 95.6%. Based on the quality standard for groundwater (GB/T 14848-93), the NO3--N concentrations in soil leachate which nitrogen application of biogas fertilizer were 20?and 60?g/(m2·a) came up to water quality standards of category III. When nitrogen application of biogas fertilizer were 100?and 140?g/(m2·a), NO3--N concentrations in soil leachate of 10% and 32.5% samples exceeded the water quality-standards of category III and it mainly occurred in June and August. The conclusion that 600?kg/(hm2·a) nitrogen application of biogas fertilizer don’t cause NO3--N pollution to groundwater based on evaluation criterion that mass concentration of NO3--N is 20?mg/L( water quality standards of category III) in leachate is arrived at.