Farmyard manure and nitrogen‒phosphorus‒sulfur fertilizers improved the yield of onion (Allium cepa L.) yield: A review article

Onion (Allium cepa L.) is a high-value vegetable crop in Ethiopia; however, its productivity remains far below the global average (8.8 vs. 19.7 t/ha). This yield gap is largely attributed to inadequate fertilization and suboptimal agronomic practices. The objective of this review is to assess the effect of different rates and combinations of farmyard manure (FYM) and NPS (nitrogen–phosphorus–sulfur) fertilizers on the yield and yield components of onion under Ethiopian conditions. Global and national research highlights that integrated nutrient management improves onion growth parameters, including plant height, leaf number, bulb size, and total yield. The combined application of FYM and NPS fertilizers enhances soil physical, chemical, and biological properties, contributing to sustainable productivity gains. In Ethiopia, the currently recommended rates 7–10 t/ha FYM and 242 kg/ha NPS have shown positive effects on crop performance. However, persistent challenges such as the variable quality of FYM, poor application techniques, non-site-specific recommendations, and limited farmer awareness undermine their effectiveness. Reviewed findings suggest that no single fertilizer type can fully address productivity constraints. Instead, the integration of organic and mineral fertilizers at optimal rates optimized to local conditions emerges as a promising approach. Future research should focus on identifying site-specific, economically viable nutrient combinations that can close the onion yield gap while enhancing soil health and long-term agricultural sustainability in Ethiopia.