Composted organic matter application is used to supply nutrients, such as nitrogen, and to accumulate carbon in the soil. However, the organic constituent dynamics derived from compost in soil have not been sufficiently clarified. The compost degradation rate depends on the adsorption forms to soil materials, such as clay and amorphous materials. A degradation test of compost using glass-fiber tube in three typical Japanese soils (Yellow soil, Gray lowland soil, and Andosol) added ¹⁵N-labeled cattle manure compost for 3 years was conducted to investigate the relationship between the degradation rate of organic constituents from compost and its adsorption form to soil materials. The changes in the constituents’ adsorption forms were analyzed by sequential extraction using three solutions (KCl, Phosphate buffer, NaOH). As a result, the KCl-extractable and phosphate buffer-extractable organic matter had a half-life of approximately 2.2 years, while the non-water-extractable (hydrophobic) organic matter had a half-life of approximately 5.3 years. Conversely, the NaOH-extractable organic matter amounts were unchanged for 3 years and accumulated about 0.25 g-N kg⁻¹ in each of the three soils. They may have gained resistance to degradation through adsorption on clay minerals and amorphous soil materials. Furthermore, the clear increase in NaOH-extractable organic matter by compost application was only 1 g-C kg⁻¹ and 0.1 g-N kg⁻¹ in soils for 3 years. Therefore, the organic matter accumulation by compost application alone is not expected. In order to accumulate more organic matter in upland soil, it is necessary to increase the adsorption sites for organic matter, which requires the addition of materials, such as clay and amorphous aluminum.

In this study, the state of nitrogen (N) flow in Japan’s food and feed supply system and livestock sector during the last four decades (1975–2015) was calculated based on material flow data without utilizing the N excretion factor of livestock. The N use efficiency (NUE = product N/feed or material N) and N loss (= N budget) to the domestic environment including agricultural lands were obtained for the food and feed supply system and livestock sector. During the period of 1975–2015, the NUE for the food and feed supply system declined (44.2%→40.5%), and nearly half of the N loss (1.22–1.71 Tg-N y⁻¹) occurred from the livestock sector. The livestock sector NUE was low, but increased (15.1%→17.4%) by improving the breeding and feeding techniques. The NUE of major livestock types improved for laying hens, broilers, and dairy cows; leveled off for pigs; and decreased for beef cattle. Around 90% of the N loss from the livestock sector occurred during the animal husbandry process and since 1990 it decreased significantly (0.76→0.60 Tg-N y⁻¹) almost in parallel with, and 0.08–0.10 Tg-N y⁻¹ higher than, the livestock excreta N in the National Greenhouse Gas Inventory Report. This difference was mainly considered to be feed loss N, of which incidence (around 10%) was about the same as that of food loss N in Japan. Our results showed that the upcycle food such as edible by-products of slaughtered animals is effective in improving livestock meat NUE; however, businesses that prioritize consumer needs and production efficiency have increased the burden on livestock bodies, leading to risk-intensive management suffering from high mortality rates, high internal organ disposal rates, increased antimicrobial resistant bacteria due to the heavy use of antibiotics, uniformity of genetic lineages, etc. The livestock sector NUE should be further improved through the promotion of healthy livestock rearing with consideration for animal welfare with consumer support.