Plant Science

We aimed to obtain the fundamental data of the fertilizer characteristics of nitrogen in liquid compost (LC), which is produced from organic wastes such as human waste and sewage sludge. The rice cultivar Hinihokari was cultivated in pots, and 5 combinations of basal fertilization and topdressing using chemical fertilizer and LC were applied in the experimental plots. Growth indicators such as plant length, the number of tillers, and the SPAD value were measured during the rice-growth season, and the amounts of nitrogen absorbed by the rice plants were estimated using these values. In addition, to understand the fertilizer characteristics of nitrogen in LC, we measured the inorganic-nitrogen concentration in the soil water. In the experimental plots in which either chemical fertilizer or LC was applied as basal fertilizer, nitrogen absorption during the initial growth stage (i.e., from transplantation to 24 days after transplantation) did not differ significantly; however, the nitrogen absorption was slightly lower in the experimental plots, in which LC was applied as the basal fertilizer. Further, the ammonium-nitrogen concentration in soil water indicated that the organic nitrogen in LC was completely mineralized at approximately 40 days after the transplantation. This phenomenon was considered to be responsible for the lowered nitrogen absorption during the initial growth stage in the plants that underwent basal fertilization with LC. In addition, in the experimental plots in which LC topdressing was applied, nitrogen absorption in the late period of rice growth (i.e., from 40 days to 55 days after transplantation) was low, and we hypothesized that the ammonium-nitrogen in LC was lost through volatilization, since the topdressing was applied to the soil surface. Further, rainfall greater than 40 mm $day^-1$ continued for 3 days after the topdressing, and leaching of the fertilizer components was suspected.