Dry matter accumulation and yield characteristics of high-nitrogen efficient rice cultivars under different ecological conditions

Objectives This study examines the dry matter accumulation, material transportation and yield of N-efficient rice cultivars in response to ecological conditions and N application levels. We aim to provide a scientific basis for selecting suitable rice cultivars in different ecological regions.

Methods Field experiments were conducted in two ecological sites; one with low light (Dayi County, Sichuan Province, DYS) and the other with sufficient light and temperature (Yongsheng County, Yunnan Province, YSY). Ten rice cultivars were used as test materials. Each cultivar was subjected to three N application levels (0, 120 and 180 kg/hm²). The rice dry matter accumulation (DMA) was measured at the jointing, heading, and maturity stages. The dry matter translocation's (DMT) contribution to yield was calculated and the rice yield was evaluated at harvest.

Results The ecological condition, N level, cultivar, and their interaction affected rice yield and dry matter accumulation. Cultivar Yixiangyou 1108 in DYS and Deyou 4923 in YSY recorded higher yield at N120 than at N180. According to GGE model analysis, Yixiangyou 1108 was a low-N-efficient cultivar, Jingliangyou 534 and F-you 498 were high-N-efficient cultivars in DYS. Deyou 4923 was a low-N-efficient cultivar, Zhongyou 295 and Fengyouxiangzhan were high-N-efficient cultivars in YSY. The DMA and DMT of high-N-efficient cultivars were affected by ecological conditions and N levels. In DYS, the yield of low-N-efficient cultivar was driven by DMA and DMT before jointing, depending on the number of effective panicles per unit area. Pre-jointing population growth rate (PGR) was significantly and positively correlated with yield (r = 0.70^**) and effective panicle number (r = 0.41^*). In DYS, high-N-efficient cultivars had (P<0.05) higher DMT after heading and growth rate from heading to maturity compared to other cultivars. Rice yield was positively correlated with PGR from heading to maturity (r = 0.56^**) and DMT after heading (r = 0.37^*). The low-N-efficient cultivar in YSY had higher PGR from jointing to heading stage, higher DMT before heading, and the 1000-grain weight was 13.61% higher than the average value in the same treatment. In YSY, high-N-efficient cultivars had high PGR from jointing to heading stage. The yield advantage correlated to the high number of spikelets per panicle. The PGR from jointing to heading had a (P<0.05) positive correlation with yield (r = 0.60^**) and spikelet number (r = 0.68^**).

Conclusions In low-light areas such as DYS, low-N-efficient cultivars' high yield is dependent on rapid PGR and high DMT before the heading stage. In contrast, high-N-efficient cultivars yield depends on high PGR and dry mater accumulation after the heading stage. In areas with adequate light and temperature, such as YSY, the higher PGR from jointing to heading stage was a common feature of low and high N efficient cultivars.