Author(s): Miriam Wanjiku, Daniel Otieno and Amina Njoroge

Abstract:
Micronutrient deficiencies, often described as hidden hunger, remain a critical global health challenge, particularly in regions dependent on cereal-based diets with limited vegetable diversity. Vegetables are a major source of essential minerals such as iron, zinc, magnesium, and calcium, yet their nutritional quality is strongly influenced by soil fertility and fertilizer management. This study evaluated the impact of polyhalite, a naturally occurring multi-nutrient mineral containing potassium, calcium, magnesium, and sulfur, on the micronutrient density of spinach (Spinacia oleracea), tomato (Solanum lycopersicum), and carrot (Daucus carota) cultivated under controlled experimental conditions. Treatments included conventional NPK fertilizer (control) and NPK supplemented with polyhalite at 100 kg ha⁻¹ and 200 kg ha⁻¹, arranged in a randomized complete block design with three replications. Micronutrient concentrations in edible tissues were analyzed using atomic absorption spectrophotometry, and results were subjected to ANOVA followed by Tukey’s HSD test. Findings revealed significant and dose-dependent increases in iron, zinc, magnesium, and calcium concentrations across all crops with polyhalite application, with the most pronounced improvements at 200 kg ha⁻¹. Spinach exhibited the largest absolute gains, while tomato showed smaller yet meaningful increases, and carrot displayed intermediate responses. These results demonstrate that polyhalite fertilization not only enhances crop quality but also contributes to human dietary improvement by enriching the mineral content of commonly consumed vegetables. The outcomes underscore the importance of multi-nutrient fertilization strategies for sustainable agriculture and nutrition-sensitive food systems. Incorporating polyhalite into household and community-level vegetable production offers a cost-effective, environmentally sound, and nutritionally significant approach to alleviating micronutrient deficiencies and strengthening food and nutrition security.