2021 Volume 92 Issue 3 Pages 238-248
In Japan, attempts have been made on rice and various vegetables to replace chemical fertilizers with methane fermentation digestates. These reports often show successful replacement of chemical fertilizers by digestates in terms of crop yields. In contrast, only a limited number of reports are available that considers the replacement effects on nutrient concentration/content of the crops and the fertilizer efficiency of digestates. This study addressed the latter issue by conducting field experiments for two years on autumn–winter radish, especially using analysis of variance with contrast. Nitrogen fertilization of 50％ and above the standard fertilization scheme following the fertilization guideline was replaced by a digestate containing approximately 2,000 mg L−1 of water–soluble ammonium nitrogen. Compared with the plots that received standard fertilization, radish in the plots applied with the digestate was grown with a limited phosphate supply attributable to low phosphate concentration in the digestate. Radish yield was lower for the group replaced with the digestate than the group fertilized solely by chemical fertilizers in the first year. In contrast, no statistical yield difference was observed between the groups in the second year. The fertilizer efficacy of the digestate for two years was estimated to be approximately 50％ compared to the standard fertilization scheme that was set as 100％. The plots where all nitrogen was basal dressed, irrespective of whether it was applied as chemical fertilizers or the digestate, contained lower amounts of soil inorganic nitrogen after harvest than those applied with nitrogen both as basal and top dressings. In the scene of fertilization by digestates, application at once as the basal dressing was considered a feasible choice from the perspective of nitrogen leaching after harvest.
