Nitrogen uptake pattern of dry direct-seeding rice and its contribution to yield in a cool temperate climate

Dry direct-seeding rice (DDSR) cultivation is expected to reduce production costs compared with transplanted rice (TPR); however, its low nitrogen (N) use efficiency (NUE) has hindered cost reduction. Additionally, polymer-coated urea application in rice cultivation is reduced for plastic pollution regulation. The split application of urea can be an alternative, but it has not been used in northeastern Japan, hence needs to be investigated. We conducted DDSR and TPR field experiments for three years using two cultivars and three or two N regimes to determine factors limiting yield and NUE using a standard cultivar ( Akitakomachi) and a high-yielding cultivar ( Yumiazusa) grown under different N regimes. The yield, yield components, and N uptake of DDSR were analyzed, and examined the contribution of N uptake until panicle initiation and heading for spikelet number by multiple regression compared to that of TPR. Additionally, we investigated the detailed N uptake pattern on DDSR until PI using the two parameters, which were calculated by exponential regression of N uptake during the vegetative period. DDSR yield was lower than that of TPR by 11% and revealed that both fertilizer recovery rate and crop NUE (yield per unit N uptake) contributed to the lower yield. N uptake until the fifth leaf age significantly influenced the N uptake until panicle initiation. DDSR yield with normal urea in this study proportion was not significantly different compared to coated urea application, indicating the possibility to be an alternative N application method.