Shuhei Morita and Shinjiro Sato, Department of Environmental Engineering for Symbiosis, Soka University, Hachioji-shi, Tokyo, Japan
Anaerobic digestion effluent (ADE) is a by-product remained after fermentation processes of organic materials for methane production. The utilization of ADE for agronomic benefits has recently been recognized as a means of reducing volume of organic wastes. Since ADE contains significant amounts of NH4-N, it can serve as a quick-releasing liquid fertilizer. However, different feedstocks yield ADE of different chemical properties, therefore it is difficult to standardize ADE as reliable and stable fertilizers.In this study, a 2-year bioassay experiment was performed to evaluate effects of different ADE derived from 4 different organic materials, namely a mixture of cow manure and food waste (CF), Mediterranean mussel (Mytilus galloprovincialis; MM), Sennin algae (Potamogeton maackianus; SA) and western waterweed (Elodea nuttallii; WW) as liquid fertilizer on Japanese mustard spinach (Brassica rapa) grown on one type of soil in the first year and 3 different types of soil in the second year. The experimental treatments were no fertilizer applied (control), chemical fertilizer applied (140-120-120 N-P2O5-K2O kg ha-1), and all 4 ADEs for the first year, and CF and SA for the second year, both applied at a rate of 14 g N m-2 in 1 L pot for two months. In addition for the second year, a treatment to mix pruned branches with ADE was added. After the harvest, pH, EC, TC, TN, NH4-N, NO3-N, TP of the soil, and dry weight (DW), TC, TN of the spinach were analyzed. From the first year results, pH, NH4-N, NO3-N and DW of all ADE-applied treatments were significantly greater than those of control. The CF-applied pot yielded the lowest DW among all treatments, and SA-applied pot the highest DW likely because SA contained the greatest amount of NH4-N. ADE with higher content of NH4-N has more potential to be used as valuable liquid fertilizer.