The 4R stewardship framework (right source, right rate, right time, and right place) is widely promoted to improve fertilizer use efficiency and sustainability in agriculture. However, within this framework, fertilizer form (i.e., the physical and chemical expression of the nutrient source) remains poorly conceptualized and inconsistently evaluated in the literature. Existing studies largely emphasize application rate, timing, and placement, while evidence on how fertilizer form governs nutrient-use efficiency (NUE), nutrient losses, and soil–plant–biological interactions remains fragmented and context-dependent. As a result, fertilizer form is often treated as a logistical input rather than a central management variable. The objective of this comprehensive review is to synthesize global evidence on how fertilizer form shapes NUE, soil chemical and biological processes, and diagnostics-driven nutrient management across cropping systems and agroecological conditions. Evidence shows that deep-placed urea and enhanced-efficiency fertilizers significantly reduce ammonia (NH3) volatilization and nitrous oxide (N2O) emissions under flooded or alkaline conditions. At the same time, monoammonium phosphate (MAP) enhances phosphorus (P) recovery compared with diammonium phosphate (DAP) in acidic or heterogeneous soils. Sulfate-based potassium fertilizers improve crop quality and reduce chloride-related stress compared with muriate of potash (MOP). In contrast, coated or organo-mineral fertilizers generally stimulate microbial activity relative to highly soluble formulations. Emerging diagnostic approaches, including mid-infrared and X-ray fluorescence spectroscopy integrated with tissue testing and on-farm trials, show promise for guiding fertilizer-form selection. However, their widespread field validation remains limited. Despite the growing adoption of advanced fertilizer forms, comparative evaluations across diverse environments remain scarce. The review highlights diagnostics and long-term field experimentation as critical priorities for advancing fertilizer-form decisions within the 4R framework.
Pierre et al. (Sun,) studied this question.