Enhancing cassava yield value and profitability through Tithonia diversifolia and cow dung applications in a tropical derived savanna Alfisol

Robust evidence linking organic amendments to cassava yield, starch content, and profitability on derived savanna sandy loam Alfisols remains limited. Therefore, field experiments were conducted in April 2021 and 2022 at the Teaching and Research Farm of Landmark University, Omu-Aran, Kwara State, Nigeria. This study was conducted to determine the effects of Tithonia diversifolia (Tithonia) and cow dung (CD) on soil physical and chemical properties, cassava performance, and economic returns. The experiment consisted of seven treatments: control, CD applied at the rate of 10 t ha^-1 (CD 10), CD applied at the rate of 20 t ha^-1 (CD 20), Tithonia applied at the rate of 10 t ha^-1 (Tithonia 10), Tithonia applied at the rate of 20 t ha^-1 (Tithonia 20), CD10 + Tithonia 10 and NPK 15-15-15 fertilizer applied at a rate of 400 kg ha^-1 arranged in a randomized complete block design with three replications. Data on the initial soil properties (bulk density, particle size, pH, soil organic matter (SOM), N, P, K, Ca and Mg), along with the chemical properties of the soil on a per-plot basis at the end of the experiment, were collected. Additionally, data on soil bulk density, porosity and moisture content were collected during the vegetative growth of the cassava. Cassava plant height, number of leaves, leaf area, tuber yield and starch content determined. Economic evaluation was conducted using partial budget analysis to estimate the gross margin per hectare for each treatment. Data collected were subjected to analysis of variance (ANOVA) using the General Linear Model procedure. Treatment means were separated using Duncan's Multiple Range Test (DMRT) at p < 0.05. Results revealed that organic amendments significantly improved bulk density, porosity, moisture content, soil organic matter, and nutrient status compared with the control and NPK fertilizer. The combined CD10 + Tithonia10 treatment produced the greatest improvements, reducing bulk density from 1.63 g cm⁻³ to 1.20 g cm⁻³ (36%), and increasing porosity from 38.5% to 54.9% (43%) and moisture content from 9.5% to 14.9% (57%) compared to the control. Average over two years, CD10 and Tithonia 10 recorded the highest values of SOM (3.19%), N (0.25%), P (20.9 mg kg⁻¹), K (0.61cmol kg⁻¹), Ca (5.67 cmol kg⁻¹), and Mg (0.91 cmol kg⁻¹), which were significantly (p < 0.05) greater than all other treatments. This improved soil environment promoted vigorous cassava growth, resulting in an increase in cassava tuber yield and starch content from 19.5 t ha⁻¹ and 21.1% in the control to 32.4 t ha⁻¹ (66%) and 48.9% (57%) respectively in the CD10 + Tithonia10 plots. In addition, CD10 + Tithonia10 produced the highest net return compared with other treatments, confirming its economic superiority. Among sole applications, Tithonia10 was the most cost-effective, delivering high yield gains at minimal input cost, making it an attractive option for resource-limited farmers. Although NPK fertilizer improved yield over the control, its high cost reduced its cost-benefit ratio (2.42) relative to organic treatments. These findings demonstrate that integrating low-cost organic amendments, particularly the combination of CD10 and Tithonia10, offers a sustainable pathway to improving cassava yield, starch quality, and farmer income while enhancing long-term soil fertility. For smallholder farmers, Tithonia10 alone represents a practical, low-cost strategy for yield improvement, whereas integrated organic applications are recommended where the goal is to maximize both economic returns and soil health.