Simulator investigation of biogas fertilizers of N on land carrying capacity

A subsurface infiltration system experiment was conducted using a soil column to investigate the N carrying capacity of turfgrass soil with different biogas fertilizer applications. The concentrations of NO₃-N and total nitrogen in the soil leachate increased with an increase in biogas fertilizer dosage. With biogas fertilizer application rates of 200 kg N/hm² (B-200) and 600 kg N/hm² (B-600), total nitrogen entrainment in leachate equaled 35.52 kg/hm² and 3.34 kg/hm², with no significant difference between the treatments. However, with applications rates of 1000 kg N/hm² (B-1000) and 1400 kg N/hm² (B-1400), total nitrogen entrainment values were 70.76 kg/hm² and 146.76 kg/hm², respectively, and significantly higher (P <; 0.05) than in the B-200 and B-600 treatments. Thus, the nitrate-nitrogen environmental risk to groundwater increased with an increase in biogas fertilizer dosage. Biogas fertilizer application presented much less risk to groundwater than did application of a chemical fertilizer at the same fertilizer application rate. Based on China´s quality standard for groundwater (GB/T 14848-93), NO₃-N concentrations in leachate under the B-200 and B-600 treatments met the category III water quality standard, whereas the test results for 10% and 32.5% of leachate samples in the B-1000 and B-1400 treatments exceeded the category III limit, respectively. Thus, considering the limitation of 20 mg/L NO₃-N in leachate as the evaluation criterion, the N carrying capacity for biogas fertilizer application was no less than 600 kg N/hm² for the turfgrass-soil subsurface infiltration system in 2009.