Smart soil fertility management for improving rice yield, nitrogen use efficiency, and greenhouse gas mitigation across South and Southeast Asia

Rice (Oryza sativa L.) provides food to more than 3.5 billion people and is cultivated on approximately 165 million hectares worldwide. Continuous intensive rice cultivation over recent decades has caused serious soil organic carbon (SOC) decline, macronutrient imbalances, and an increase in greenhouse gas (GHG) emissions, primarily methane (CH₄) and nitrous oxide (N₂O). Almost all smallholder systems rely on conventional fertilizer management, resulting in critically low nitrogen use efficiency (NUE). However, integrated systems-level evidence of the synergistic performance of smart soil health management practices (SSHMPs) across regions and agro-ecological contexts remains limited. A systematic review with narrative synthesis, following PRISMA 2020 and the Synthesis Without Meta-analysis (SWiM) guideline, a systematic search of five electronic databases (Web of Science, Scopus, PubMed, Google Scholar, and FAO AGRIS) was conducted, yielding 240 records. Following duplicate removal and systematic screening, 109 studies encompassing peer-reviewed field experiments, meta-analyses, review articles, and technical reports were included in this review. Site-specific nutrient management (SSNM) and the Nutrient Expert® (NE®) tool improved rice yield by 6–18% and NUE by 20–117% over farmer practice. Integrated nutrient management (INM) increased grain yield by 8–28% and SOC by 14–60% in long-term trials. Controlled-release urea reduced ammonia losses by 23–62%. Alternate wetting and drying (AWD) irrigation reduced global warming potential (GWP) by about 20–36%, primarily through lower methane (CH₄) emissions, with generally no yield penalty, although this benefit can be partly offset by higher nitrous oxide (N₂O) emissions, depending on water and nitrogen management. In Bangladesh, urea deep placement (UDP) raised yield by 10–21% while saving 25–33% of nitrogen. SSHMPs offer real potential for rice productivity, NUE and GHG mitigation, but their performance is context-dependent and subject to trade-offs. The novel contribution of this review is an integrated conceptual framework, supported by a structured semi-quantitative cross-technology synthesis, linking soil fertility technologies to productivity, nutrient cycling, soil organic carbon, greenhouse gas balance, soil health and adoption constraints. Scaling them requires coordinated policy and targeted extension.