The objective of this study was to identify an application strategy for a blend of two controlled-release nitrogen fertilizers (CRNFs) that optimized yield and N-use efficiency of late japonica rice in the Yangtze River Delta. In a two-year field experiment using high-yield split-applied urea (CK) and no-N fertilization as control (N0), nine CRNF treatments were evaluated for their effects on grain yield, N uptake (N_UP), soil ammonium nitrogen (NH₄⁺-N) dynamics, and ammonia volatilization (AV). The treatments included sulfur-coated urea (SCU), urease inhibitor urea (AHA), 90-d polymer-coated urea (P₉₀), 120-d polymer-coated urea (P₁₂₀), and five BBFs prepared by mixing CRNFs at a 3:7 ratio (AHAP₉₀, SP₉₀, AHAP₁₂₀, SP₁₂₀, and P₉₀P₁₂₀). Based on N release characteristics, CRNFs were categorized into four release modes: pre-positioned single-peak (PrSRM), post-positioned single-peak (PoSRM), decreasing double-peak (DDRM), and increasing double-peak (IDRM). Synchronization between soil NH₄⁺-N dynamics under CRNFs and plant N uptake rate (N_UPR) under CK was quantified using dynamic time warping (DTW), with smaller values indicating higher synchrony. Results showed that single-peak release modes significantly reduced grain yield and N_UP by 12.6% and 10.5%, respectively. The IDRM treatment, a blend of 90-d and 120-d polymer-coated urea, showed NH₄⁺-N supply dynamics most closely matching the N demand of high-yielding rice, with lower two-year average DTW values (SSR_DTW 1.01, N_UPS_DTW 1.72) than DDRM (1.03 and 2.00), which translated into increases in spikelet number, grain yield, and N_UP by 4.49%, 6.03%, and 4.85%, respectively, while decreasing AV by 86.7% compared with CK. One-time application of IDRM fertilizer can align soil NH₄⁺-N supply with rice N demand, ensure high yield, and reduce N losses, providing an optimized fertilization strategy for sustainable rice production in the Yangtze River Delta.

Rice productivity faces critical sustainability challenges from stagnating yields and inefficient fertilizer use, particularly in intensive agricultural regions like the Yangtze River Delta (YRD) of China. Controlled-release blended fertilizers (CRBF), which synchronize nutrient release with crop demand, represent a promising strategy to enhance rice productivity. Here, we conducted an eight-year (2017–2024) field study across 25 representative sites in the YRD to evaluate CRBF’s effects, complemented by a regional extrapolation analysis. Our findings showed that, relative to conventional fertilization, CRBF increased rice yield by 4.9%, primarily by increasing the number of effective panicles (5%) and plant biomass (5.2%–11.3%). Notably, this yield benefit rose to 5.3% when CRBF was applied via deep placement, which was attributed to greater root biomass (13.1%–29.2%) and higher soil NH₄⁺-N availability (24.3%–43.6%), thereby enhancing N uptake. Furthermore, initial soil organic matter was identified as the predominant modulator of CRBF effectiveness. Regional extrapolation projected that applying CRBF could enhance rice yield by 4.0% across the YRD, with deep placement providing an additional 2.1% gain. In conclusion, our study demonstrates that adopting CRBF, particularly with deep placement, is a robust and effective strategy to sustainably boost rice productivity in intensive rice cultivation systems.

One-time application of controlled-release blended fertilizer (CRBF, a mixture of five nitrogen (N) fertilizers in a certain ratio) can achieve high yield and N use efficiency (NUE) in rice (Oryza sativa L.). However, the effects of CRBF with one-time application on root spatial distribution and physiological characteristics remain unclear. We measured the effects of CRBF with one-time application on rice yield, NUE, root morphology and growth, and N uptake capacity in field and root box experiments. Six N treatments were set up: no nitrogen (N₀), high-yield three-split application of urea as a control (CK), urea (U) with broadcast, U with side-deep fertilization, CRBF with broadcast, and CRBF with side-deep fertilization. Our findings showed that root characters were positively correlated with yield and NUE. Compared to CK and U treatments, CRBF with one-time applications increased root characters (including root biomass, root N uptake, root activity, and the expression level of ammonium transporters) at tillering and heading stages. The root length, surface area and volume in the 0–10 cm soil layer enhanced under CRBF with one-time applications at tillering stage, and in the 0–20 cm soil layer at the heading stage. This contributed a 5.96%–39.40% and 3.69%–16.87% increase in plant dry matter accumulation and N uptake, and a 2.08%–18.28% and 14.60%–149.57% increase in yield and NUE, in 2022 and 2023, respectively. Taken together, our findings showed that one-time application of CRBF could increase rice yield and NUE by optimizing the root morphology distribution and N uptake.

Single-time fertilization (STF) with controlled release blended fertilizer (CRBF) improves grain yield and nitrogen use efficiency (NUE) in rice production. However, the impact of soil nitrogen (N) distribution and root growth on rice yield and NUE under STF with CRBF remains unclear. Here, a two-year field experiment investigated the effects of two fertilizer types (normal urea (U) and CRBF) and two single-time fertilization methods (broadcast and side-deep fertilization) on the soil N distribution, plant N uptake, root characteristics, grain yield, and NUE. The results showed that CRBF under STF increased the averages of plant dry matter accumulation, N uptake, grain yield, nitrogen recovery efficiency (NRE), and nitrogen agronomic efficiency (NAE) by 8.29, 21.85, 10.57, 79.28, and 74.8% compared to the other treatments, respectively. Side-deep fertilization with CRBF further increased NUE by 12.78% compared to broadcast. Moreover, CRBF under STF increased the leaf SPAD value and glutamine synthetase (GS)/glutamine oxoglutarate aminotransferase (GOGAT) activity by 5.93 and 25.58%, respectively. CRBF under STF increased the soil inorganic N concentration and showed a “rising early and stabilizing later” pattern. In addition, CRBF under STF improved rice root growth and increased the averages of root biomass, total root number, root average diameter, total root length, total root surface area, and total root volume by 28.30, 28.56, 18.64, 13.38, 35.26, and 37.06%, respectively, at the tillering and heading stages. Partial least squares path modeling indicated that CRBF under STF increased the soil inorganic N concentration which improved root morphology, thereby increasing N uptake and improving the rice yield and NUE. Taken together, our findings show that CRBF with single-time fertilization is the preferred N fertilizer strategy for achieving high yield and efficiency in rice, and that side-deep fertilization is the optimal fertilization method.

Synchronizing the nitrogen (N) supply of slow- and controlled-release N fertilizers (SCRNFs) with rice N demand is essential in replacing multiple urea applications with a single basal application of SCRNFs. Traditional assessment of N supply characteristics primarily examines N release patterns, which are limited to coated SCRNFs and disregard N transformation mechanisms, necessitating a more universal and reliable index. Based on the capacity of crop N status to detect N deficiency or excess, we hypothesized that utilizing leaf N balance index (NBI) as a measure of N status could offer novel insights into assessing N supply characteristics of SCRNFs. Field experiments were conducted with four individual SCRNFs-humic acid urea (HAU), sulfur-coated urea (SCU), urease inhibitor urea (UIU), and polymer-coated urea (PCU) and their four combined forms, alongside high-yield urea split application as control (CK). The results revealed that NBI dynamics relative to CK reflected the N supply potential of different SCRNFs while categorizing them as short-, medium-, and long-acting fertilizers. Combinations incorporating the long-acting SCRNF (PCU) consistently demonstrated superior performance in yield (by 5.5%) and N use efficiency (by 42.8%) through providing more consistent and efficient N supply throughout the rice growth cycle. Grain yield exhibited negative correlation with the difference in NBI dynamics between SCRNFs and CK, suggesting that synchronizing N supply between one-time application of SCRNFs and conventional high-yield fertilization is crucial for high yield. These findings demonstrate the potential of N status diagnosed by leaf NBI to evaluate N supply characteristics of SCRNFs and highlight the importance of synchronized N supply for a one-time SCRNF application.

Controlled-release urea (CRU) is widely reported to supply crop nitrogen (N) demand with one basal application, thus effectively replacing split applications of urea without diminishing grain yield and N use efficiency (NUE). However, its use for replacement for high-yield split applications of urea (CK) for rice is untested. In addition, the degree to which greenhouse gas (GHG) emissions in rice systems are affected when CRU is substituted for CK remains unclear. During 2017 and 2018, we sampled plant growth and gas emissions in a rice paddy field treated with three CRU types (sulfur-coated urea [SCU], polymer-coated urea [PCU], and bulk blended CRU [BBU]) applied via two methods (surface broadcasting on the soil and subsurface banding at 5 cm depth), with CK as a control. The three CRUs led to different soil NH₄⁺-N dynamics, and the N supply pattern under BBU was more beneficial for rice seedling establishment than under SCU and PCU, resulting in grain yield and NUE comparable to those under CK. CRU type showed no significant effect on either CH₄ emissions or N₂O emissions, and broadcast CRUs exhibited significantly higher total GHG emissions than CK. However, banded CRUs significantly reduced the total GHG emissions in comparison with broadcast CRUs, by 9.2% averaged across the two years. Reduced CH₄ emissions, particularly during the period prior to the middle drainage, contributed largely to the GHG difference. With comparably high grain yield and low total GHG emissions, banded BBU showed a low yield-scaled GHG (GHG emissions divided by grain yield) comparable to that under CK in both years. Overall, our study suggested that N management synchronized with rice demand and contributing to a high NUE tended to minimize yield-scaled GHG. Broadcast CRU can hardly substitute for CK in terms of either grain yield or GHG emissions, but banded BBU is a promising N management strategy for sustaining rice production while minimizing environmental impacts.

Nitrogen (N) fertilization increases rice yield, but inappropriate N fertilizer application increases N loss and the risk of environmental pollution. Short-term fertilizer postponing (FP) generally reduces N apparent surplus and increases rice yields, but the effects of long-term FP on N surplus and rice yields remain unknown. Our study was the first to investigate the impacts of long-term FP (11 years) on N apparent surplus and rice yields. FP effects in the short term (≤6 years) did not affect rice yields, whereas FP effects in the long term (>6 years) increased rice yields by 13.9% compared with conventional fertilization (CF). FP did not affect panicles per unit area, 1000-kernel weight, and filled-kernel rate, but spikelets per panicle increased over time due to spikelet formation stimulation. FP also reduced the N apparent surplus over time more strongly than CF owing to higher N accumulation and N utilization efficiency. FP effects in the long term also significantly increased soil organic matter, total N, and NH₄⁺-N content. Our results were supported by a pot experiment, showing that rice yields in soils with a history of FP were significantly higher than those for soils without a history of FP, indicating that FP increased rice yields more strongly in later years mainly because of soil quality improvement. Our findings suggest that long-term FP can reduce N loss while increasing rice yields by improving soil quality.

Straw incorporation is a global common practice to improve soil fertility and rice yield. However, the effect of straw incorporation on rice yield stability is still unknown, especially under high fertilization level conditions. Here, we reported the effect of straw returning on rice yield and yield stability under high fertilization levels in the rice–wheat system over nine years. The results showed that straw incorporation did not significantly affect the average rice yield of nine years. Straw incorporation reduced the coefficient of variation of rice yield by 25.8% and increased the sustainable yield index by 8.2%. The rice yield positively correlated with mean photosynthetically active radiation (PAR) of rice growth season and the effects of straw incorporation on rice yield depended on the PAR. Straw incorporation increased the rice yield by 5.4% in the low PAR years, whereas it did not affect the rice yield in the high PAR years. Long-term straw incorporation lowered soil bulk density but improved the soil organic matter, total N, available N, available P, and available K more strongly than straw removal. Our findings suggest that straw incorporation can increase rice yield stability through improving the resistance of rice plant growth to low PAR.

In rice–wheat rotation systems, crop straw is usually retained in the field at land preparation in every, or every other, season. We conducted a 3-year-6-season experiment in the middle–lower Yangtze River Valley to compare the grain qualities of rice under straw retained after single or double seasons per year. Four treatments were designed as: both wheat and rice straw retained (WR), only rice straw retained (R), only wheat straw retained (W), and no straw retained (CK). The varieties were Yangmai 16 wheat and Wuyunjing 23 japonica rice. The results showed contrasting effects of W and R on rice quality. Amylopectin content, peak viscosity, cool viscosity, and breakdown viscosity of rice grain were significantly increased in W compared to the CK, whereas gelatinization temperature, setback viscosity, and protein content significantly decreased. In addition, the effect of WR on rice grain quality was similar to that of W, although soil fertility was enhanced in WR due to straw being retained in two cycles. The differences in protein and starch contents among the treatments might result from soil nitrogen supply. These results indicate that wheat straw retained in the field is more important for high rice quality than rice straw return, and straw from both seasons is recommended for positive effects on soil fertility.

Improvement of yield in rice (Oryza sativa L.) is vital for ensuring food security in China. Both rice breeders and growers need an improved understanding of the relationship between yield and yield-related traits. New indica cultivars (53 in 2007 and 48 in 2008) were grown in Taoyuan, Yunnan province, to identify important components contributing to yield. Additionally, two standard indica rice cultivars with similar yield potentials, Ⅱ You 107 (a large-panicle type) and Xieyou 107 (a heavy-panicle type), were planted in Taoyuan, Yunnan province and Nanjing, Jiangsu province, from 2006 to 2008 to evaluate the stability of yield and yield-related attributes. Growth duration (GD), leaf area index (LAI), panicles per m² (PN), and spikelets per m² (SM) were significantly and positively correlated with grain yield (GY) over all years. Sequential path analysis identified PN and panicle weight (PW) as important first-order traits that influenced grain yield. All direct effects were significant, as indicated by bootstrap analysis. Yield potential varied greatly across locations but not across years. Plant height (PH), days from heading to maturity (HM), and grain weight (GW) were stable traits that showed little variation across sites or years, whereas GD (mainly the pre-heading period, PHP) and PN varied significantly across locations. To achieve a yield of 15 t ha^-1, a cultivar should have a PH of 110–125 cm, a long GD with HM of approximately 40 days, a PN of 300–400 m^-2, and a GW of 29–31 mg.