Factors controlling available soil nitrogen in Japanese paddy fields

• Published in: Soil science and plant nutrition (Tokyo) Vol. ahead-of-print; no. ahead-of-print; pp. 1 - 12
• Main Authors: Ichinose, Yuri, Ise, Yuta, Kanda, Takashi, Maejima, Yuji, Yagi, Tetsuo, Takahashi, Yoshinori, Nakagawa, Shinpei, Kamiyama, Kiyomi, Iwasa, Hirokuni, Kadokura (Kaneko), Ayako Kadokura, Ohashi, Yoshinori, Komatsu, Shigeo, Matsuyama, Minoru, Hirayama, Yusuke, Mochida, Toshiyuki, Matsui, Kayo, Takimoto, Takahiro, Obara, Hiroshi, Kubotera, Hideo, Takata, Yusuke
• Format: Journal Article
• Language: English
• Published: Kyoto Taylor & Francis 02.11.2023; Taylor & Francis Ltd
• Subjects: Land use; Nitrogen; Organic matter; Paddy soil; paddy-upland rotation; rice; Rice fields; Rotation; Soil fertility; Soil properties; Soil surveys; Soil temperature; Soil texture; Soil types; Soils; soybean; Texture; Japan
• ISSN: 0038-0768; 1747-0765
• DOI: 10.1080/00380768.2023.2231013

Available soil nitrogen (Av-N) is an important indicator for understanding the soil fertility in paddy fields. Previous studies have reported a decline in Av-N resulting from paddy-upland rotation at a regional scale in Japan, while the factors influencing this phenomenon on a national scale are not well understood. This study aims to assess the effects of soil temperature, land use, soil type and soil texture on Av-N in paddy fields across Japan. Soil surveys were conducted in 13 prefectures in 2020 and 2021, involving the collection of soil samples from the plow layer in a total of 2,600 paddy fields. Our results revealed that soil temperature had the most significant influence on Av-N, followed by land use and soil type. Av-N exhibited a negative correlation with soil temperature, whereby the average Av-N in the thermic soil temperature regime (>15°C, Av-N: 107 ± 48 mg kg −1 ) significantly lower than that in the mesic soil temperature regime (≤15°C, Av-N: 166 ± 74 mg kg −1 ). Increased upland frequency in paddy fields led to a decrease in Av-N, particularly pronounced in the thermic soil temperature regime, while partially mitigated in the mesic soil temperature regime. In the thermic soil temperature regime, paddy fields with long-term upland usage (upland frequency of paddy fields was more than 50%) had an average Av-N of 50 mg kg −1 , necessitating additional organic matter application. Furthermore, the results concerning soil type and soil texture indicated that Av-N was higher in wet soil compared to semi-wet soil, and fine-textured soil had higher Av-N than medium-course textured soil. These findings underscore the negative effect of accelerated drying in paddy fields due to the expanding practice of paddy-upland rotation, leading to decreased Av-N. In conclusion, our study proposes the importance of organic matter management practices, with a primary emphasis on soil temperature, further refined by considering land use and soil type, to ensure the maintenance of adequate Av-N levels in paddy fields in Japan.