Optimizing Soil Fertility and Crop Productivity Using Biodigestate, Poultry Manure, and NPK Integration

Abstract

The integration of biodigestate with either inorganic fertilizer or organic manure, such as poultry manure, plays a vital role in improving crop productivity. To evaluate the effects of these amendments, a screenhouse experiment was conducted to assess the impact of biodigestate, poultry manure, and NPK fertilizer on soil chemical properties, as well as the growth, yield, and mineral composition of okra ( Abelmoschus esculentus L. Moench) and cucumber ( Cucumis sativus L.). The study included seven treatments: biodigestate (BD), poultry manure (PM), NPK 15–15–15 fertilizer (NPK), biodigestate + poultry manure (BD+PM), biodigestate + NPK fertilizer (BD+NPK), NPK fertilizer + poultry manure (NPK+PM), and a control with no amendments. The experimental layout followed a completely randomized design (CRD) with three replications. The okra and cucumber trials were conducted simultaneously in adjacent sections of the same screenhouse. Amendments were applied at a rate of 120 kg N ha⁻¹. Findings indicated that the application of BD, PM, or NPK—either individually or in combination—significantly enhanced soil chemical properties, plant growth, yield, and mineral composition of both crops compared to the control. NPK, PM, and BD increased the fruit weight of cucumber and okra by 100.0% and 50.0%, 240.0% and 150.0%, and 196.7% and 103.3%, respectively, relative to the control. Among the sole applications, PM demonstrated the most substantial improvements in soil fertility and crop performance compared to BD and NPK. Compared to NPK and BD, PM increased the yield of cucumber and okra by 67.2% and 66.7%, and 14.0% and 25.0 %, respectively. Additionally, the combination of NPK+PM (1.49 kg of cucumber and 0.12 kg of okra) resulted in better soil properties, growth, and yield than BD+NPK (0.74 kg of cucumber and 0.07 kg of okra). However, BD+PM (1.42 kg of cucumber and 0.12 kg of okra) performed comparably to NPK+PM, while exhibiting the highest nutrient composition in both okra and cucumber fruits. The BD+PM combination offers a viable alternative to NPK+PM, achieving similar yields while improving okra and cucumber nutrient content. The novelty of this study lies in its dual-crop, side-by-side assessment of BD-based nutrient management strategies under controlled conditions—a methodological approach not widely adopted in previous research. By simultaneously evaluating BD interactions with both organic and inorganic sources across two fruit vegetables, this work provides new evidence supporting BD+PM as a viable and sustainable alternative to conventional NPK-based fertilization. Future research should investigate the effects of these amendments on fruit quality attributes such as taste, shelf life, and nutrient stability.