The excessive application of nitrogen (N) fertilizer can result in soil and water pollution, thereby negatively impacting the ecological environment. However, reducing the amount of N fertilizer may lead to a decrease in crop yield. Two years’ experiment (2021 and 2022) investigates the influence of one-time reduced basal application of controlled-release N fertilizer (CRU) and increased planting density on the grain yield and N utilization characteristics of mechanically transplanted japonica rice. Nanjing 5718 was used as the experimental material. Under the condition of 225 kg ha⁻¹ of N, three controlled-release periods of CRUs (60d, 80d, 100d) and three planting densities (6, 8, and 10 seedlings/hole) were combined, totaling nine combinations. Moreover, a conventional split fertilization treatment with 300 kg ha⁻¹ of N and a planting density of 4 seedlings/hole was set as the control (CK). The yield, dry matter accumulation, N accumulation, and N utilization efficiency were evaluated. The research findings demonstrate that the CRU80-6 treatment exhibited the highest efficacy among all N reduction and density increase treatments, resulting in a significant yield increase of 3.1–10.3% compared to other treatments. After the jointing stage, the CRU80-6 treatment exhibited the highest dry matter accumulation compared to other treatments, with an increase ranging from 0.8% to 13.6%, and was significantly lower than that of the CK by 4.3% to 5.0%. The N accumulation and translocation traits of the CRU80-6 treatment closely resembled those of CK. However, both N recovery efficiency (NRE) and N agronomic efficiency (NAE) exhibited a remarkable increase compared to CK, with an average enhancement in NRE of 30.01%. Therefore, we contend that the CRU80-6 treatment, with a 25% reduction in N input, can ensure efficient N utilization and attain a relatively stable grain yield.

This paper aims to clarify the effects of different exogenous phytohormones on the physiological traits of rice (Oryza sativa L.) at the early stage of irrigation under low-temperature stress. In this study, two types of rice varieties with different temperature sensitivities screened out previously, namely, a cold-tolerant variety (Nan Jing 9108) and a low-temperature-sensitive variety (Hui Liang You 898), were used in pots to simulate the process of low-temperature stress in rice at the early stage of grouting (6–9 days after anthesis) with artificial low-temperature treatments. The experimental treatments were 450 mg L⁻¹ Methyl jasmine acid (MJ), 46 mg L⁻¹ Melatonin (MT), 69 mg L⁻¹ Salicylate (SA), 40 mg L⁻¹ Erythromycin (GA₃), 25 mg L⁻¹ Zeatin (Z), 145 mg L⁻¹ Spermidine (SPD), and 5 mg L⁻¹ Abscisic acid (ABA) sprayed on rice before low-temperature stress, while low-temperature treatment without spraying (DK) and conventional planting without spraying (CK) were added as the control. The results showed that compared with the room temperature control (CK, sprayed with deionized water), the low-temperature control (DK, low-temperature treatment, and sprayed with deionized water) all significantly reduced the rice grain yield. Different exogenous hormones sprayed before low-temperature stress could increase rice yield, among which, Z and SPD spraying treatments had a better effect on the yield of Hui Liang You 898, while different exogenous hormone treatments increased the yield of Nan Jing 9108 in an average manner. The Z and SPD treatments increased the yield of Hui Liang You 898 by 24.87% and 26.16% and that of Nan Jing 9108 by 15.87% and 17.80%, respectively. This was mainly attributed to the significant increase in thousand-grain weight and fruiting rate, while there was no significant difference in the number of spikes and number of grains. The different exogenous hormone treatments were able to delay leaf senescence, enhance the photosynthetic production capacity of plants by increasing leaf chlorophyll content, and thus increase the accumulation of photosynthetic assimilation products and population growth rate after flowering. Among them, both Z and SPD treatments resulted in a population growth rate of more than 30% from spike flushing to maturity, which led to a higher dry matter accumulation of the plant at maturity. In addition, in the dry matter distribution of the plant at maturity, the seeds occupied a higher accumulation amount and proportion compared with the respective DK; the SPD treatment resulted in the maximum distribution rate of seeds at maturity of Hui Liang You 898, with an increase of 8.27%, and the Z treatment resulted in the maximum distribution rate of seeds at maturity of Nan Jing 9108, with an increase of 7.34%. At the same time, the Z treatment significantly increased the activities of adenosine diphosphate glucose phosphorylated enzyme (AGP) and starch branching enzyme (SBE) in the grains of both varieties, which resulted in the accumulation of more starch and ultimately increased the rice grain yield. The results verified that different exogenous phytohormones could be used to regulate the insufficiency of grouting caused by low-temperature stress during the grouting and fruiting stages of rice and enriched their agronomic and physiological traits in response at the same time.

The carbon and nitrogen (N) metabolism of rice under different mid-stage N compensation timings is unclear. Two Japonica super rice cultivars were examined under four N compensation timings (N1-N3: N compensation at mid-tillering, panicle initiation, and spikelet differentiation. N0: no N compensation) and CK with no N application. Mid-stage N compensation increased the N concentrations of various tissues, and N2 showed the highest plant N uptake at both the heading stage, maturity, and the grain filling period. Among the treatments, N2 showed the highest N utilization efficiency. With delayed compensation timing, there was a gradual decrease in soluble sugar and starch concentrations in each tissue, accompanied by a decline in the non-structural carbohydrate (NSC) concentration. Specifically, N2 treatment exhibited the highest NSC accumulation and the remobilized NSC reserve, but NSCs per spikelet decreased with delayed compensation timing. The highest yield was also obtained with N2, exhibiting a 4.5% increase compared to the N0 treatment, primarily due to an improvement in spikelets per panicle. Conclusively, N compensation at the panicle initiation stage is a reasonable N management strategy that can coordinate the improvement of carbon and N metabolism, enhance N accumulation with efficient utilization and NSC accumulation, and ultimately increase the yield.

This study addresses the uncertainty regarding the potential of a one-time basal application of mixed nitrogen (N) fertilizer to optimize both yield and eating quality of late-maturing medium japonica rice Nangeng 9108 and Fenggeng 1606 in the Yangtze River Delta. Six distinct combinations of blended N fertilizers were evaluated, with conventional split fertilization serving as the control. The blended formulations combined controlled-release N fertilizer (CRNF) and quick-acting N fertilizer (CNF) at a 1:1 ratio. Furthermore, the CRNF component was a combination of two CRNF types with varied N-release durations at a 4:1 ratio, leading to treatments labeled A1, A2, B1, B2, C1, and C2. Over a 2-year study, treatments B1, B2, C1, and C2 matched or surpassed the control in grain yield, with C1 and C2 yielding 2.83–4.85% more. Among the above high-yield treatments, C1 showcased the best rice eating quality, which exhibited increased peak viscosity, hot viscosity, cool viscosity, breakdown, and taste value of milled rice, and a decrease in rice protein content (PC). This enhancement in quality correlated with N accumulation patterns and their interplay with sink capacity. Specifically, a higher N accumulation resulted in a robust sink capacity under the C1 treatment, thus reducing N availability per unit sink capacity (NAV) and rice PC, ultimately enhancing the overall palatability of milled rice. Conclusively, the C1 fertilizer blend demonstrates potential in concurrently boosting yield and eating quality of late-maturing medium japonica rice in the region.