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Controlled-release urea (CRU) releases nitrogen (N) at the same pace that rice takes it up, which can effectively improve N use efficiency, increase rice yield and improve rice quality. However, few studies have described the effects of CRU application on the photosynthetic rate and endogenous enzyme activities of rice. Accordingly, a two-year field trial was conducted with a total of seven treatments: CK, no N fertilizer; BBF, regular blended fertilizer; RBBF, 20% N-reduced regular blended fertilizer; CRF1, 70% CRU+30% regular urea one-time base application; CRF2, 60% CRU+40% regular urea one-time base application; RCRF1, CRF1 treatment with 20% N reduction; and RCRF2, CRF2 treatment with 20% N reduction. Each treatment was conducted in triplicate. The results showed that the N recovery efficiency (NRE) of the controlled-release bulk blending fertilizer (CRBBF) treatments was significantly greater over the two years. There were significant yield increases of 4.1–5.9% under the CRF1 treatment and 5.6–7.6% under the CRF2 treatment compared to the BBF treatment, but the differences between the reduced-N treatments RBBF and RCRF2 were not significant. Photosynthetic rates under the CRF1 and CRF2 treatments were significantly higher than under the other treatments, and they had significantly greater RuBPCase, RuBisCO, glutamate synthase (GOGAT) and glutamine synthetase (GS) enzyme activities. Additionally, the soil NH4+-N and NO3−-N contents under the CRBBF treatments were significantly higher at the late growth stage of rice, which was more in-line with the fertilizer requirements of rice throughout the reproductive period. CRBBF also led to some improvement in rice quality. Compared with the BBF and RBBF treatments, the protein contents under the CRBBF treatments were reduced but the milling, appearance, eating and cooking qualities of the rice were improved. These results showed that the application of CRBBF can improve the NRE, photosynthetic rate and endogenous enzyme activities of rice, ensuring sufficient N nutrition and photosynthetic material production during rice growth and thereby achieving improved rice yield and quality.

Abstract The search for an effective zinc fertilizer and its application method to effectively increase zinc content and enhance aroma in rice grains is a crucial objective. In this study, a 2-year field plot experiment was conducted to investigate the influence of ZnO NPs foliar spraying on rice quality, grain zinc and aroma content, along with exploring the physiological mechanisms underlying these effects. Our results demonstrated that the rice breakdown value and taste value of foliar spraying zinc oxide nanoparticles were improved by 31.0–41.7% and 8.2–13.0% compared with CK (control treatment involved spraying water), improving the tasting and steaming quality of rice. While Fe and Cu content in grains decreased for the application of zinc oxide nanoparticles, zinc oxide nanoparticles foliar spraying significantly increased the zinc content and accumulation of grains by 33.6–65.1% and 37.8–74.7%, respectively. Further analysis showed that the sprayed zinc oxide nanoparticles achieved effective enrichment of zinc in edible parts and increased the final bioavailability of Zn. In addition, foliar spraying of zinc oxide nanoparticles significantly increased activities of nitrate reductase and glutamine synthetase in leaves, which elevated nitrogen content in leaves and grains, and ultimately enhanced 2-acetyl-1-pyrroline (2-AP) content in grains at maturity by 6.1–21.4% compared to CK. Our findings indicated that zinc oxide nanoparticles can be practically applied as a foliar fertilizer at the gestation for quality improvement, zinc enrichment and aroma enhancement of rice grains.

Zinc oxide nanoparticles (ZnO NPs) have been widely used in agriculture as a new type of Zn fertilizer, and many studies were conducted to evaluate the effect of ZnO NPs on plant growth. However, there are relatively few studies on the effects of application methods and appropriate dosages of ZnO NPs on rice yield, quality, grain Zn content, and distribution. Therefore, in the 2019 and 2020, field trials were conducted with six ZnO NPs basal application dosages of no ZnO NPs, 3.75 kg hm−2, 7.5 kg hm−2, 15 kg hm−2, 30 kg hm−2, and 60 kg hm−2, and the effects of ZnO NPs application on rice yield, quality, grain Zn content, and distribution were investigated. The results demonstrated that applying ZnO NPs in Zn-deficient soils (available Zn < 1.0 mg kg−1) increased rice grain yield by 3.24%–4.86% and 3.51%–5.12% in 2019 and 2020, respectively. In addition, ZnO NPs improved the quality of rice by increasing the head milling rate, reducing chalky grain percentage, and increasing the taste value and breakdown of rice. In terms of Zn accumulation in rice, ZnO NPs application significantly increased the Zn content in both milled rice and brown rice, compared with no Zn treatment, in 2019 and 2020, Zn content in milled rice significantly increased by 20.46%–41.09% and 18.11%–38.84%, respectively, and in brown rice significantly increased by 25.78%–48.30% and 20.86%–42.00%, respectively. However, the Zn fertilizer utilization gradually decreased with increasing ZnO NPs application dosage. From the perspective of yield, rice quality, Zn fertilizer utilization, and Zn accumulation, basal application of 7.5 kg–30 kg hm−2 ZnO NPs is beneficial for rice yield and quality improvement and rice Zn accumulation. This study effectively demonstrated that ZnO NPs could be a potential high‐performed fertilizer for enhancing rice yield, quality, and zinc content of edible grain fraction synergistically.

Zinc deficiency in rice can lead to reduced nutritional value and taste. This study investigates the potential of zinc oxide nanoparticles (ZnO NPs) as a foliar fertilizer during the jointing stage to improve rice yield, quality, and grain zinc enrichment. Over a two-year field experiment (2019–2020), six doses of ZnO NPs (ranging from 0 to 12 kg hm−2) were applied during the jointing stage (46 days after transplanting). The results revealed that foliar spraying of ZnO NPs increased the number of spikelets per spike and the thousand-grain weight by 7.4% to 9.2% and 4.2% to 7.1%, respectively, resulting in a substantial increase in rice yield. Furthermore, it led to a reduction in chalky white and chalky whiteness by 6.23% to 23.6% and 2.2% to 27.9%. ZnO NPs effectively boosted zinc content in rice grains while decreasing the phytic acid to zinc ratio, indicating improved zinc enrichment. Remarkably, protein and amylose content remained unaffected. These findings underscore the potential of ZnO NPs as a foliar fertilizer to enhance rice production, quality, and zinc enrichment. Further research can explore optimal application strategies and long-term effects for sustainable rice production.