New indica and japonica hybrid rice cultivars, such as the Yongyou series, provide farmers with very high yield potential. However, information on their canopy light capture and solar radiation use efficiency in the late season is limited. Field experiments were performed to compare the radiation-use parameters of four rice types: indica rice (IR), inbred japonica rice (IJR), hybrid japonica rice (HJR), and hybrid indica/japonica rice (HIJR), from 2016 to 2018 during the late season in Hangzhou, China. The grain yield, aboveground biomass, intercepted solar radiation (SI), and radiation-use efficiency (RUE) of the HIJR were on average respectively 13.4%–53.4%, 14.3%–30.6%, 7.6%–21.4%, and 8.2%–14.9% higher than those of the HJR, IJR, and IR. The leaf area index (LAI) of the HIJR was 18.2%–57.0% greater than that of the IJR and HJR at four growth stages, resulting in respectively 17.8%–38.5% and 10.7%–42.8% greater canopy light interception rates (LIR) and amount of intercepted solar radiation during the vegetative stage. The prolonged grain-filling stage also led to respectively 33.9%–52.6% and 30.5%–51.4% increases in amounts of incident and intercepted radiation for the HIJR relative to the IR during grain filling. These results indicate that the SI superiority of the HIJR was caused by canopy closure as rapid as that of the IR during the vegetative stage (greater LAI and canopy LIR during the growing season) and a grain-filling stage as long as that of the HJR. For grain-filling stage, differences in leaf P_n between HIJR, IR, and IJR were not significant, suggesting that the greater RUE of the HIJR (12.7%–52.8% higher) than that of the other rice types resulted from improved canopy architecture after flowering (FL). Principal components analysis (PCA) revealed that the superiority of the HIJR in terms of solar radiation use resulted from the greater canopy light capture capability of IR and the prolonged growth period (especially during grain filling) of japonica rice in the late growing season.

To evaluate the effects of various rotation systems on rice grain yield and N use efficiency, a paddy–upland cropping experiment (2013–2016) was conducted in southeastern China. The experiment was designed using six different rice––winter crop rotations: rice–fallow (RF), rice–wheat (RW), rice–potato with rice straw mulch (RP), rice–green manure (Chinese milk vetch; RC–G), rice–oilseed rape (RO), and rice–green manure crop (oilseed rape with fresh straw incorporated into soil at flowering; RO–G) and three N rates, N0 (0 kg N ha⁻¹), N1 (142.5 kg N ha⁻¹), and N2 (202.5 kg N ha⁻¹). Average rice yields in the RF (5.93 t ha⁻¹) rotation were significantly lower than those in the rotations with winter crops (7.20–7.48 t ha⁻¹) under the N0 treatment, suggesting that incorporation of straw might be more effective for increasing soil N than winter fallow. The rice yield differences among the rotations varied by year with the N input. In general, the grain yields in the RP and RO–G rotations –were respectively 11.6–28.5% and 14.80–37.19% higher than those in the RF in plots with N applied. Increasing the N rate may have tended to minimize the average yield gap between the RF and the other rotations; the yield gaps were 18.55%, 4.14%, and 0.23% in N0, N1, and N2, respectively. However, the N recovery efficiency in the RF was significantly lower than that in other rotations, except for 2015 under both N1 and N2 rates, a finding that implies a large amount of chemical N loss. No significant differences in nitrogen agronomic efficiency (NAE) and physiological efficiency (NPE) were found between the rotations with legume (RC–G) and non–legume (RO and RW) winter crops, a result that may be due partly to straw incorporation. For this reason, we concluded that the return of straw could reduce differences in N use efficiency between rotations with and without legume crops. The degree of synchrony between the crop N demand and the N supply was evaluated by comparison of nitrogen balance degree (NBD) values. The NBD values in the RP and RW were significantly lower than those in the other rotations under both N1 and N2 rates. Thus, in view of the higher grain yield in the RP compared to the RW under the N1 rate, the RP rotation might be a promising practice with comparable grain yield and greater N use efficiency under reduced N input relative to the other rotations. The primary yield components of the RF and RP were identified as number of panicles m⁻² and numbers of kernels panicle⁻¹, respectively. The NAE and NPE were positively correlated with harvest index, possibly providing a useful indicator for evaluating N use efficiency.