Effects of organic nutrient sources and NPK fertilizer on soil fertility, yield, and rhizome quality of ginger

Soil fertility improvement using locally available nutrient sources is essential for sustainable ginger production in low-input tropical agroecosystems. A two-year field study was conducted in 2023 and 2024 at two sites in Owo, Ondo State, southwestern Nigeria, to evaluate the comparative effects of animal manures, green biomass amendments and NPK fertilizer on soil properties, growth, yield and rhizome quality of ginger ( Zingiber officinale Roscoe). Eight treatments comprising pig manure, cow dung, poultry manure, goat manure, Tithonia diversifolia , Chromolaena odorata , NPK 15-15-15 fertilizer and an unfertilized control were arranged in a randomized complete block design with three replications. All nutrient sources were applied at an equivalent rate of 120 kg N ha − 1 . Data were subjected to analysis of variance, and treatment means were separated using Duncan’s multiple range test at p ≤ 0.05. Organic amendments generally increased soil pH, organic matter, total N, available P and exchangeable K, Ca and Mg, while reducing bulk density and improving soil moisture compared with the control and NPK fertilizer. Poultry manure produced the highest rhizome yields of 20.5 and 21.8 t ha − 1 in 2023 and 2024, respectively, and generally recorded the highest growth, dry matter, leaf nutrient concentrations and rhizome protein, ash, fat, oleoresin and mineral contents, whereas carbohydrate and fibre contents were greatest in the control. Tithonia diversifolia and Chromolaena odorata generally ranked next to poultry manure. Organic amendments therefore improved soil fertility, ginger productivity and rhizome quality more effectively than sole NPK fertilizer in the forest-savanna transition zone of southwest Nigeria.