OICC Press International Journal of Recycling of Organic Waste in Agriculture 2251-7715 2026 08 05 Syenite Powder as a Sustainable Alternative Potassium Source for Maize and Bean Production in Tropical Soils 10.57647/ijrowa.2026.t1rm.0162 EN Camile Figueiredo Oliveira Federal Institute of Mato Grosso do Sul, Nova Andradina-MS, Brazil – 79750-000 Caroline Figueiredo Oliveira Selleri Federal University of Grande Dourados, Faculty of Agricultural Sciences, Dourados, MS, Brazil, 79825-070 Nericlenes Chaves Marcante Mineragro Agronomic Research and Development, Brasília, DF, Brazil, 73020-406 Danilo Marques França Mineragro Agronomic Research and Development, Brasília, DF, Brazil, 73020-406 and University of Brasília, Brasília, DF, Brazil, 70910-900 Éder de Souza Martins Embrapa Cerrados, Planaltina, DF, Brazil, 73310-970 Elcio Ferreira Santos Federal Institute of Mato Grosso do Sul, Nova Andradina-MS, Brazil – 79750-000 Journal Article 2026 08 05 Purpose: Syenite powder is a potential alternative source of potassium (K) for tropical agriculture, where reliance on imported fertilizers increases costs and environmental impacts. This study evaluated the agronomic efficiency of syenite powder as a sustainable K source for maize (Zea mays L.) and bean (Phaseolus vulgaris L.) grown in contrasting tropical soils. Method: A 60-day soil incubation study and a subsequent greenhouse experiment were conducted using two soil types (Typic Quartzipsamment and Oxisol) and five K rates (0, 100, 200, 400, and 800 mg dm⁻³) supplied by syenite or a commercial glauconitic siltstone fertilizer. After incubation, maize and beans were cultivated in the same pots. Plant growth (dry matter, height, and stem diameter), shoot nutrient accumulation, and residual soil fertility were evaluated. Results: Syenite increased K availability in both soils, following a linear release pattern similar to that of the commercial fertilizer. It enhanced plant growth and K uptake, which showed quadratic responses to increasing application rates. In maize, the highest syenite rate increased biomass by up to sixfold in Typic Quartzipsamment and raised shoot K content by 9%. In beans, K accumulation doubled at 400 mg dm⁻³ compared with the commercial source. Post-harvest soil K levels were similar among treatments, while syenite also increased soil pH, Ca, and P without affecting Mg availability. Conclusion: Syenite powder proved to be an effective and sustainable K source, comparable to conventional fertilizers in its ability to improve plant growth and nutrient uptake in tropical soils. Its gradual nutrient release supports long-term soil fertility and may reduce dependence on imported fertilizers, thereby enhancing environmental and economic sustainability. Highlights ·        Syenite can act as an alternative potassium source for maize and common bean ·        Syenite is compared with a commercial fertilizer as a K source ·        Syenite increases soil K availability similarly to the commercial fertilizer ·        Maize biomass increases sixfold and bean K accumulation doubles at 400 mg dm⁻³ ·        Syenite shows agronomic performance comparable to the commercial K fertilizer