Molecular Soil Biology 2025, Vol.16, No.6, 325-334 http://bioscipublisher.com/index.php/msb 332 7.2 Knowledge gaps in irrigation-fertilization synergy research Most studies only set 2~4 irrigation levels (e.g., 70~160 mm evapotranspiration replenishment, FC60-FC100, CPE60-100%) and 3–5 fertilizer treatments. While this can reveal response curves under moderate deficit and normal irrigation, it is difficult to characterize thresholds and failure points under extreme environmental stress conditions (e.g., extreme high temperature and drought, extreme waterlogging). Most water and fertilizer experiments focus on N and P supply and a small amount of organic fertilizer substitution, while the hydraulic effects of K, S, trace elements, layered fertilization (e.g., shallow-deep double-layer application), and root-pore structure coupling have only been preliminarily quantified under a few mechanical direct seeding conditions using CT imaging. Most water and fertilizer studies use yield, oil content, WUE, and NUE as end-point indicators, and quantitative analysis of ecological consequences such as greenhouse gas emissions, soil carbon pool evolution, and long-term background nutrient supply (INuS) changes remains insufficient (Yousaf et al., 2017). 7.3 Future applications and observational research directions Utilize CROPGRO-Canola to derive optimal regional nitrogen fertilizer ranges under long-term time series and different price scenarios (e.g., the long-term optimal range for Central China is 120~160 kg N ha-1), and combine this with random forest analysis to decompose the relative importance of natural and socioeconomic factors (e.g., spring rapeseed yield is affected by natural and economic factors by approximately 47% and 53%, respectively) (Liang et al., 2023), to construct regionalized recommendations for water and fertilizer management systems in different ecological zones. Long-term field experiments and a crop rotation system perspective are needed, for example, systematically tracking the 10-year scale effects of different NPK ratios on yield, soil inorganic nitrogen (INuS), and environmental risks in rice-rapeseed rotation. Existing 2-year experiments have shown that unbalanced fertilization significantly reduces soil nutrient supply capacity and amplifies dependence on nitrogen. Layered fertilization, drip/micro-irrigation, conservation tillage, and high-throughput root phenotyping and electrical characterization (e.g., root capacitance and impedance) should be combined to simultaneously diagnose root water and nitrogen uptake capacity and lodging risk. Future research should combine field water and fertilizer optimization with simple measures accessible to farmers (e.g., drainage, flood control, straw mulching, small-scale rainwater harvesting facilities) through cross-site observation networks and "yield gap" analysis. Long-term observation and modeling of irrigation quotas, limited irrigation in the late season, and drought-tolerant genotype combinations are necessary in arid and semi-arid regions. Acknowledgments The author thanks the anonymous reviewers for their constructive comments and suggestions, which was very helpful in improving this manuscript. Conflict of Interest Disclosure The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. References Ahmadi M., and Bahrani M., 2009, Yield and yield components of rapeseed as influenced by water stress at different growth stages and nitrogen levels, American-Eurasian Journal of Agricultural and Environmental Science, 5: 755-761. Amiri S., Yarnia M., Mirshekari B., Farahvash F., and Rashidi V., 2024, Restricted Irrigation Regimes and Rapeseed High-Yielding Genotypes Can Be Applied to Cope With the Water Shortage Crisis and More Stable Oil Production. Journal of Crop Health, 76: 917-927. https://doi.org/10.1007/s10343-024-00995-9 Bouchet A., Laperche A., Bissuel-Belaygue C., Snowdon R., Nesi N., and Stahl A., 2016, Nitrogen use efficiency in rapeseed. A review, Agronomy for Sustainable Development, 36: 1-20. https://doi.org/10.1007/s13593-016-0371-0 Eyni‐Nargeseh H., AghaAlikhani M., Rad S., Mokhtassi‐Bidgoli A., and Sanavy S., 2019, Late season deficit irrigation for water-saving: selection of rapeseed (Brassica napus) genotypes based on quantitative and qualitative features, Archives of Agronomy and Soil Science, 66: 126-137. https://doi.org/10.1080/03650340.2019.1602866 Feng J., Hussain H., Hussain S., Shi C., Cholidah L., Men S., Ke J., and Wang L., 2020, Optimum Water and Fertilizer Management for Better Growth and Resource Use Efficiency of Rapeseed in Rainy and Drought Seasons. Sustainability. https://doi.org/10.3390/su12020703
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