The objectives of the present study were to characterize the spatial patterns of net nitrogen mineralization and nitrification by focusing on the gap/canopy mosaic structure in an old-growth beech-oak forest on Mt. Hakusan, Japan. We observed high spatial variations in soil net nitrogen mineralization (2.7–94.7 kg-N ha⁻¹ period⁻¹) and nitrification rates (0.1–31.1 kg-N ha⁻¹ period⁻¹) with averages of 24.6 kg-N ha⁻¹ period⁻¹ and 4.9 kg-N ha⁻¹ period⁻¹, respectively during a field incubation period of 135 days. In addition, the nitrification ratio for nitrogen mineralization exhibited high spatial variation that ranged from 0.9％ to 91.5％ and averaged 24.3％. The net nitrogen mineralization, nitrification rates, and canopy openness parameters showed a significant positive correlation with inorganic nitrogen content (NO₃-N and NH₄-N), soil bulk density, and nitrogen input to the soil. In contrast, these parameters displayed a significant negative correlation with the C : N ratio of the soil. Furthermore, the canopy openness exhibited a significant positive correlation with net nitrogen mineralization and nitrification rates. These results suggest that structural heterogeneity, which is the gap/canopy mosaic structure, influenced the soil net nitrogen mineralization and nitrification rates in the old-growth forest on Mt. Hakusan.

This study aimed to determine from soil-based evidence when the traditional shaded cultivation system that used rice straw and reed screens in tea plantations was established in Uji, Kyoto, Japan. A soil pit was excavated close to the tea tree that was considered the oldest indigenous species in the only surviving rice-straw and reed-screen tea plantation called “Uji Shichimeien.” The pedon, which represented Okunoyama tea plantation soils, was described and carbon contents and phytolith compositions were examined. Humin fractions were dated using AMS radiocarbon (¹⁴C) dating. The carbon content began to increase upwards in the soil at the Bw (sample no. 8)–AB (sample no. 7) horizon boundary, and it further incrementally increased above the AB (sample no. 6)–A (sample no. 5) horizon boundary. Phytolith remains, which originated from Oryza (including rice), were found in the AB horizon and such phytoliths increased upwards at the AB–A horizon boundary. However, the phytoliths originating from natural vegetation (excluding those from Oryza) decreased upwards from the AB horizon to A horizon. The AMS ¹⁴C dating yielded calibrated dates (standard deviation of 2σ) of 1341–1396 cal AD (probability=56.9％) with a median date of 1369 AD on the humins in the upper part (sample no. 6) of the AB horizon, and 1396–1440 cal AD (probability=90.8％) with a median date of 1418 AD on the humins in the lowest part (sample no. 5) of the A horizon. Therefore, the traditional shaded cultivation system in the oldest existing tea plantation in Uji (the Okunoyama tea plantation) was estimated to have been established in the first half of the 15th century, and this was approximately 150 years before the second half of the 16th century that was previously inferred from data from historical documents.

The fertilizer conversion factor is used to calculate the amount of available nutrients in organic matter, and it is indispensable for estimating the total amount of chemical fertilizer to be applied to crop fields. Although a guideline to use the factor for single applications is available, it does not exist for consecutive applications to maize (Zea mays L.) fields. This study aims to determine the nitrogen fertilizer conversion factor for cattle manure and slurry applied in consecutive years to maize fields. We performed a burying field test in which nitrogen in manure and slurry was found to decompose over 5 years. In a 6-year cultivation test, the amount of hot-water extractable nitrogen, which is an indicator of soil nitrogen fertility, declined over the study period in some treatment plots. Moreover, the degree of this decrease was lower in some manure-applied plots. After the second year, the fertilizer conversion factors of manure and slurry from the start of consecutive applications were often higher than the current standard values (0.20 for manure and 0.40 for slurry), which were estimated after single application to maize fields. Additionally, the increase in fertilizer conversion factors of both manure and slurry may be related to the cumulative amount of organic nitrogen that was input. Our results indicate that the nitrogen fertilizer conversion factors in maize fields were 0.30 and 0.50 for manure and slurry, respectively after more than 3 or 4 consecutive years of application. Considering the organic nitrogen content in common manure and slurry from this area, we suggest that the use of a nitrogen fertilizer should be reduced after the 5th year of consecutive manure or slurry application.

One of the uses of spent coffee grounds (SCG) is its incorporation into agricultural field soils. However, their effect on N₂O emission and microbial N₂O production processes are not well understood. We conducted outdoor pot and soil incubation experiments to quantify the effect of SCG application on N₂O emission from andosol and to elucidate the relationship between N₂O emission and microbial N₂O production processes after SCG application. We cultivated spinach in the pot experiment and applied fertilizer in both the experiments at a rate in accordance with the local practice.

In the pot experiment, we observed a large decrease in N₂O emission from with SCG (WC) treatment as compared with those without SCG (NC) treatment between 5 and 21 days after SCG application. Cumulative N₂O emission over 70 days of the pot experiment was significantly lower in the WC treatment than in the NC treatment. Furthermore, soil ammonium oxidation potential was lower in the WC treatment compared with the NC treatment throughout the experimental period. The results of acetylene inhibition experiment suggested that the reduction of N₂O to N₂ was larger in the WC treatment than in the NC treatment. Moreover, the effect of SCG application on N₂O emission in the soil incubation experiment was not consistent among different WFPS (water-filled pore space). In the WFPS60％, the WC treatment tended to have higher N₂O emission compared with the NC treatment. However, in the WFPS90％, N₂O emission from the WC treatment was lower than that from the NC treatment. Our results suggest that SCG application decreases N₂O emission from andosol by changing both nitrification and denitrification in comparison with that of the NC treatment, although its effectiveness could vary with WFPS condition. This study also showed that SCG application tends to decrease crop yield.