Biogas fertilizer carrying capacity of a turfgrass-soil subsurface infiltration system

In order to test the land carrying capacity of biogas fertilizer application, a subsurface infiltration system using a soil column experiment was carried out and the effect of different amounts of biogas fertilizer application was investigated by measuring the leachate. The total nitrogen concentration of tested biogas residues was 2.8%, TN, NH₄-N, NO₃-N, TP of tested biogas slurry was 1730~3450 mg/L, 1328~2892 mg/L, 37~173 mg/L and 51~213 mg/L. The results showed that the concentrations, concentration of NO₃-N was in the soil leachate increased with increase in biogas fertilizers dosage. With the same fertilizer application rate (20 g N/m²), the land carrying capacity of using biogas fertilizer was much higher than that of chemical fertilizer application in wet year, however, with the similar land carrying capacity in dry year. Based on the quality standard for ground water (GB/T 14848-93), 2009 was a wet year, the concentrations for NO₃-N in leachate under 20 g N/m² (B-20) and 60 g N/m² (B-60) treatments met category III water quality-standards. When the concentrations of NO₃-N in 100 g N/m² (B-100) and 140 g N/m² (B-140) treatments were tested, 10% and 32.5% of water samples of leachate exceeded the limitation of the water quality-standards (category III), which mainly occurred during June to August in 2009. 2010 was a dry year, whole treatments were reached category III water quality-standards except B-140. In conclusion, with the quality standard for ground water (GB/T 14848-93), the limitation of the 20 mg/L NO₃-N in leachate as evaluation criterion, land carrying capacity of N for biogas fertilizers application was more than 600 kg N/hm² for turf grass-soil subsurface infiltration system in 2009, while was more than 600 kg N/hm² in 2010.