Inbred varieties outperformed hybrid rice varieties under dense planting with reducing nitrogen

Abstract

Field experiments were conducted over two years to evaluate the effects of planting density and nitrogen input rate on grain yield and nitrogen use efficiency (NUE) of inbred and hybrid rice varieties. A significant interaction effect was observed between nitrogen input and planting density on grain yield. Higher number of panicles per square meter and spikelets per panicle largely accounted for the observed advantage in performance of inbred, relative to hybrid varieties. Compared with high nitrogen input rate, nitrogen absorption efficiency, nitrogen recovery efficiency, and partial factor productivity increased by 24.6%, 28.0%, and 33.3% in inbred varieties, and by 32.2%, 29.3%, and 35.0% in hybrids under low nitrogen input, respectively. Inbred varieties showed higher nitrogen absorption efficiency, nitrogen recovery efficiency, and partial factor productivity than hybrids, regardless of nitrogen input level. Nitrogen correlated positively with panicle number, spikelets per panicle, biomass production at flowering, and after flowering in inbred varieties but only with panicle number and biomass production at flowering in hybrids. Inbred varieties are more suitable for high planting density at reduced nitrogen input regarding higher grain yield and NUE. These findings bear important implications for achieving high yield and high efficiency in nutrient uptake and utilization in modern rice-production systems.

Figure 1

Daily maximum and minimum temperatures and solar radiation during the rice-growing season at Jingzhou in 2017 (a) and Hangzhou in 2018 (b).

Figure 2

Correlation matrix of various grain yield parameters and biomass in inbred rice (n = 42). N, nitrogen application rate; D, planting density; P, panicles m^-2; S, spikelets per panicle; GF, percent seed set; GW, 1,000-grain weight; DMF, dry matter production at flowering; DMAF, dry matter production after flowering; Y, grain yield. Numbers are determination coefficients. *P < 0.05. **P < 0.01.

Figure 3

Correlation matrix of various grain yield parameters and biomass in hybrid rice (n = 48). N, nitrogen application rate; D, planting densities; P, panicles m^-2; S, spikelets per panicle; GF, percent seed set; GW, 1,000-grain weight; DMF, dry matter production at flowering; DMAF, dry matter production after flowering; Y, grain yield. Numbers are determination coefficients. *P < 0.05. **P < 0.01.