Effects of Co-Application of Animal Manures, Chromolaena odorata and NPK Fertilizer on Soil Properties, Carrot Yield and Nutrient Content in a Tropical Agroecosystem

Enhancing soil quality and crop productivity through sustainable nutrient management is crucial for agricultural sustainability. This study assessed the impacts of organic manures (poultry manure (PM), cattle manure (CM), swine manure (SM), goat manure (GM), Chromolaena odorata (Chromolaena) and NPK fertilizer, applied individually or in combination, on soil properties, carrot (Daucus carota L.) growth, yield, and nutrient content. The treatments were arranged in a randomized complete block design with three replications. Results showed that organic manures significantly improved soil physical properties by reducing bulk density, increasing porosity, and enhancing moisture content, with GM being the most effective due to its higher organic carbon content (31.8%). Carrot yield was more influenced by soil physical properties than by chemical attributes. Among the treatments, PM produced the tallest plants (24.5 cm) and the most leaves (12.6), while GM resulted in the largest root diameters (1.4 cm), longest roots (22.1 cm), and heaviest root weights (40.6 t ha-1). The combined application of organic manures and NPK fertilizer exhibited synergistic effects, improving both soil physical properties and nutrient availability. The GM+NPK combination recorded the highest root yield (45.6 t ha-1) in 2021 and (45.9 t ha-1) in 2022 and enhanced Vitamin A (β-carotene) and Vitamin C (ascorbic acid) contents. The co-application of organic manures and NPK fertilizer, as an integrated nutrient management approach, consistently proved superior to the sole application of either input by improving soil fertility and reducing dependence on chemical fertilizers, making it a viable strategy for sustainable carrot production in tropical regions.