Abstract:

The low price of rice has placed farmers in a cost-price squeeze, and extravagant nitrogen application in rice agriculture has resulted in a decrease in nitrogen uptake and utilization efficiency and serious environmental pollution. This has caused scientists to pay more and more attention to rice nitrogen uptake and utilization efficiency. These field experiments were conducted using indica hybrid rice (Oryza sativa) to explore the genetic potentiality of increasing nitrogen uptake and utilization efficiency. Seven parameters of nitrogen uptake and utilization, TNA (Total nitrogen accumulation), NDMPE (Nitrogen dry matter production efficiency), NGPE (Nitrogen grain production efficiency), NTE (Nitrogen transportation efficiency), NHI (Nitrogen harvest index), NAE (Nitrogen agronomy efficiency) and NRE (Nitrogen recovery efficiency), were measured. Results showed that there were significant or highly significant differences in these seven parameters among genotypes, except for TNA and NDMPE at tillering of early season rice, TNA at heading of early season rice and NTE at late season rice. Long growth duration could increase TNA, NDMPE, NGPE, and NAE. NDMPE, NGPE, NAE, NRE and NHI for hybrid rice were higher than for inbred rice. The seven parameters of two-line hybrid rice and three-line hybrid rice were almost equal at early season, and NGPE, NHI, NAE, NRE and TNA of two-line hybrid rice were smaller than that of three-line hybrid rice at late season. This indicated that both nitrogen uptake and utilization efficiency of two-line rice were not increased.Ranking methods were employed in order to make an exact valuation for nitrogen uptake and utilization efficiency of genotypes. Ranking results indicated that there were great differences among different parameters and between early and late season rice in the same parameter. The genotypes were ranked according to the means of the seven parameters after standard transformation, which provided a way for comprehensive valuation of nitrogen uptake and utilization efficiency of the genotypes. Considering the difference in integration ranking of genotypes at early and late season, a coincidence index (square root of means of square of integration ranking difference of identical genotypes at early and late season) was employed to evaluate the coincidence degree of integration ranking of genotypes at early and late season. Results showed that, of 30 genotypes, integration rankings of `Zhongyou 253’,’Zaoxiang 1’,’`Guyou 11’ and ’65396’ at early and late season coincided well, and of the seven parameters, integration rankings of NDMPE at early and late season coincided well.