Fate of N and Relative Efficiency of ¹⁵N-labeled organic materials applied to transplanted rice in Northern Kyushu region of Japan

Seven kinds of ¹⁵N-labeled organic materials were applied to transplanted rice to investigate their N fate and relative efficiency in the northern Kyushu region of Japan. The ¹⁵N labeled organic materials examined in a micro-plot experiment were cattle manure compost, poultry manure compost, swine feces, rice straw compost, rice bran, rice straw, and wheat straw. Regarding swine feces, rice bran, and wheat straw, the direct evaluation of their N fate in paddy fields using ¹⁵N organic materials has not been reported. A significant difference in the N fate in response to the type of organic materials was observed in the uptake rate by rice plants. The uptake rate at the maturity stage was significantly higher in poultry manure (29%), swine feces (25%), and rice bran (26%) than for the other organic materials (6–13%). Cattle manure compost showed the lowest value, namely 6–7%. Using the uptake rate of e5NH4) 2S04 observed earlier, the relative efficiency of organic materials (relative uptake rate of organic material N to chemical fertilizer N) was calculated as the index of the organic material N efficiency. These relative efficiencies of organic materials derived from animal wastes were 16–19, 81, 72, and 71% for cattle manure compost, poultry manure compost, poultry manure compost without inherent NH₄-N, and swine feces, respectively, and were similar to those estimated by indirect way. The relative efficiencies of organic materials derived from plant residues were 25–31, 73, 33, and 34% for rice straw compost, rice bran, rice straw, and wheat straw, respectively. The N uptake from the organic materials (OM-N uptake) in swine feces and cattle manure compost continued throughout the rice growth period, whereas the OM-N uptake of the other organic materials declined remarkably after 54 DAT. No significant difference was observed in the residual rate and the loss rate among the organic materials. However, some tendencies that might be related to the properties of the organic materials could be revealed, such as the high residual rate of rice straw compost and the high loss rate of cattle manure compost and rice straw.