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Fertilizer-derived nitrogen use of two varieties of single-crop paddy rice: a free-air carbon dioxide enrichment study using polymer-coated 15N-labeled urea

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journal contribution
posted on 25.11.2021, 14:00 by Kentaro Hayashi, Takeshi Tokida, Miwa Arai, Hidemitsu Sakai, Hirofumi Nakamura, Toshihiro Hasegawa

Atmospheric concentrations of carbon dioxide (CO2) have steadily increased over recent decades. The fertilization effect of elevated CO2 concentrations (E-[CO2]) is known to increase the biomass production and also the nitrogen (N) demand of paddy rice, which affects the rice N use efficiency. This study was conducted to elucidate the fertilizer-derived N use of paddy rice (Oryza sativa L.) for two varieties, japonica cv. Koshihikari and indica cv. Takanari, with and without E-[CO2] using a free-air CO2 enrichment (FACE) facility in central Japan. To quantify the fate of fertilizer-derived N directly, polymer-coated 15N-labeled urea was used with a one-shot application rate of 80 kg N ha–1 incorporated into the plowed layer at the basal fertilization before transplanting of rice seedlings. The biomass, total N concentrations, and 15N abundance in each part of the rice plants were measured at the panicle initiation, heading, and maturing stages. The total N content and 15N abundance in the soil were measured at the maturing stage to evaluate the N balance of the rice–soil system. While E-[CO2] significantly increased the whole plant biomass and the total N content in panicles, it did not increase the total N and the fertilizer-derived N content in the whole plant. The recovery efficiency (fertilizer-derived N in the whole plant to applied N, RE) ranged between 64.9% and 68.7%, and the agronomic efficiency (fertilizer-derived N in panicles to applied N, AE) ranged between 37.8% and 43.8%. The effect of CO2 on RE and AE was not significant. The REs, higher in Koshihikari, and the AEs, higher in Takanari indicated that Takanari preferentially allocated fertilizer-derived N to panicles. The REs, 69% at the maximum in this study, implies an upper limit of use efficiency of N fertilizer, even for polymer-coated (controlled-release) fertilizer. E-[CO2] significantly increased the rice N uptake from sources other than fertilizer, of which mineralization was the most-likely source. Monitoring of soil fertility and appropriate fertilization management are, therefore, necessary for sustainable rice production avoiding long-term decline in soil N fertility.

Funding

This study was supported by a Grant-in-Aid for Scientific Research, No. 26252061 provided by the Japan Society for the Promotion of Science. Tsukuba FACE was established and maintained by ‘Development of technologies for mitigation and adaptation to climate change in Agriculture, Forestry and Fisheries,’ a project provided by the Ministry of Agriculture, Forestry and Fisheries, Japan. This study was also supported by the Research Institute for Humanity and Nature (RIHN: a constituent member of NIHU), Project No. 14200156;JSPS[Grant-in-Aid for Scientific Research No. 26252061];

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