[P1] Field Crop Production

[P1-07] Analysis of the N Uptake Pattern to Improve Increasing Yields of Dry Direct-Seeding Rice in a Cool Climate

*Nominated for Presentation Awards

^○Mari Namikawa^1,2, Toshihiro Hasegawa¹, Takayuki Yabiku¹, Toshinori Matsunami¹ (1.Tohoku Agricultural Research Center, National Agriculture and Food Research Organization, Japan, 2.Crop Science Laboratory, United Graduate School of Agricultural Sciences, Iwate University, Japan)

Dry direct-seeded rice (DSR) is a promising alternative to reduce labor costs compared to transplanted rice, but its low nitrogen (N) fertilizer use efficiency is one of the constraints to the efficient management of DSR in a cool climate. To explore reasons for low NUE in northern Japan, we examined the N uptake patterns of DSR under three different fertilizer regimes under three environments: two years in Morioka and one in Hanamaki, Iwate Prefecture, Japan. We used two cultivars ('Akitakomachi' and 'Yumiazusa') in Morioka and one ('Moeminori') in Hanamaki. In all N treatments at both sites, N uptake patterns exhibited the initial exponential growth (phase 1) followed by a linear growth (phase 2) as a function of the accumulated effective thermal index (AETI). These patterns are well characterized by four parameters: N uptake at the 5th leaf age (NLA5), Relative Nitrogen Uptake Rate (RNR) in phase 1, breakpoint AETI at which the pattern shifts from the exponential to linear phase (Nbreak+a AETI), and the constant rate of N uptake in phase 2 (a). Nitrogen treatments had significant effects on NLA5, RNR and a. Multiple regression analysis revealed that the three parameters had significantly positive effects on grain yield, but NLA5 and RNR had greater effects than a. We, therefore, conclude that the N uptake pattern during the exponential growth phase imposes the major limitation to yield. NLA5 differed between environments suggesting initial growth/soil conditions also play a role in controlling early growth and thus grain yields.