Fertilizer efficacy of concentrated and carbonized materials derived from methane fermentation digested slurry and their effect on greenhouse gas emission

Methane fermentation is a promising biomass utilization technology, but diposing of the digested slurry is a serious problem. Since digested slurry contains nitrogen, phosphate and potassium, it may be used as agricultural amendments. To improve the value of digested slurry as agricultural amendments, concentration and carbonization were conducted. But fertilizer efficacy of concentrated or carbonized slurry is not clear. This dissertation aims to evaluate the fertilizer efficacy of : (1) 'digested liquid' (concentrated liquid part of digested slurry), (2) 'biochar' (carbonized solid part of digested slurry) and (3) 'digested liquid attached biochar'. Because application of biochar is said to reduce greenhouse gas emission, the N2O and CO2 emission from applying 'digested liquid' and 'biochar' were measured. 'Digested liquid', which contains a lot of ammonium nitrogen and potassium, was applied as fertilizer to tomato plants. The growth, yield and amounts of nitrogen uptake of tomatoes applied with digested liquid were equal to those of chemically- fertilized tomatoes. While nitrogen present in inorganic fertilizers assumed to be potentially 100% available to the plant, this was similar for digested liquid which seemed to have 100% efficacy. 'Biochar' contains a lot of citric acid -soluble phosphate which was evaluated for its phosphorus fertilizer efficacy in Japanese mustard spinach. The results showed that biochar's phosphorous fertilizer efficacy was equal or even more than that of the chemical phosphorus fertilizer. 'Digested liquid attached biochar' contains nitrogen, and higher amounts of phosphate and potassium. Nitrogen is low because 30% of ammonium nitrogen contained in digested liquid was volatilized or changed state that is not extracted by 100 g /L potassium chloride solution, when digested liquid was attached to biochar. After applying digested liquid and biochar, to field-grown Japanese mustard spinach, N2O and CO2 flux from the soil was monitored. Digested liquid had similar effects on N2O and CO2 flux with that of chemical fertilizer. On the other hand, application of biochar increased N2O and CO2 flux from the soil.