Evaluation of nitrogen nutrition characteristics of different rice cultivars at seedling stage

Excessive application of nitrogen (N) fertilizers leads to nitrogen loss and increases the cost of agricultural production. Screening rice cultivars with high N efficiency is an effective approach to improving N use efficiency and reducing environmental pollution. In this paper, hydroponic experiments were conducted to examine the differences in N absorption and accumulation of 55 rice cultivars (lines) at seedling stage. The experiments used the same N dose of 40 mgL1 in the form of both NH₄⁺-N and NO₃^–-N and the evaluation indices standardized using subordinate function of interval 0, 1. The 55 rice cultivars (lines) were classified based on N use efficiency and hierarchical cluster analysis. There were significant differences in aboveground biomass, including whole plant stem, leaf and root, as well as N content in roots, stems and leaves of the rice cultivars (lines) between treated with NH₄⁺-N and NO₃^–-N (P < 0.05). Also the ranges of coefficients of variation were 0.690.80 and 0.570.74, respectively, for NH₄⁺-N and NO₃^–-N treatments. Factor analysis showed that the principal com- ponents of the NH₄⁺-N and NO₃^–-N treatments were the same. The first principal component was mainly reflected biomass indices and N accumulation, determined using the whole plant, stem, leaf and root biomass, as well as accumulated N in the whole plant, stem and leaf and root. The second principal component was determined using N content. By combining variation characteristics and factor analysis of N uptake and accumulation in rice, the whole plant biomass, stem and leaf biomass, root biomass, stem and leaf N accumulation were used as indices to evaluate high N use efficiency potentials of rice cultivars (lines) at seedling stage. Calculation of the comprehensive values of N use efficiency, based on the membership function method and fitted hierarchical clustering chart of squared Euclidean distance, showed that the 55 rice cultivars (lines) grouped into three categories — high, medium and low N use efficiencies. Rice cultivars (lines) with high, medium and low N use efficiencies with NH₄⁺-N and NO₃^–-N treatments accounted for 10.91%, 27.27% and 61.82% of the total rice cultivars (lines), respectively. The whole plant biomass, stem and leaf biomass, root biomass, stem and leaf N accumulation could be used as indices to evaluate the N use efficiency potentials of rice cultivars (lines) at seedling stage. ‘Guangliangyou 3905’, ‘Yongyou 9’, ‘Zhongxian 2503’, ‘Ⅱyou 602’, ‘Liangyou 766’ and ‘Shenliangyou 1813’ rice cultivars had high N use efficiency under both NH₄⁺-N and NO₃^–-N treatments.