Aim of the study:
Although supplementary irrigation (SI) systems have emerged as a potential solution to mitigate the impact of drought spell in crop production, there is a lack of comprehensive research that specifically analyze the gross margin associated with the use of supplementary irrigation systems for okra and chili pepper production. The aim of this study was to evaluate the efficiency and to conduct cost-benefit analysis of SI systems in the production of the studied crops in northern Ghana.

Material and methods:
The study was a 4 × 2 × 2 factorial design with three replications, using the Randomized Complete Block Design (RCBD). The research treatments were: 4 levels of NPK fertilizer, rainfed and supplementary irrigation (SI) with spray tubes irrigation system. NPK was applied at a rate of 0 kg ∙ ha⁻¹ (control), 150, 200, 250 kg ∙ ha⁻¹, and 0 kg ∙ ha⁻¹ (control), 100, 150 and 200 kg ∙ ha⁻¹ for okra and chili pepper respectively.

Results and conclusions:
The results revealed that chili pepper produced a marketable yield of 2067.41 kg ∙ ha⁻¹ in SI and 1441.60 kg ∙ ha⁻¹ in rain-fed cultivation. Regarding okra cultivation, SI gave a marketable yield of 1415.70 kg ∙ ha⁻¹ whereas 1135.10 kg ∙ ha⁻¹ was obtained from rainfed plots. For chilli pepper, at an average cost of USD 1324.80/ha and USD 1146.70/ha, a gross margin (GM) of USD 516.40/ha and USD 137.00 was attained for SI and rainfed cultivation, respectively, representing a statistically significant difference at 5% (p < 0.006). In the case of okra, a cost of USD 1540.20/ha and USD 1362.20 was invested in SI and rain-fed cultivation system respectively, and a gross margin (GM) of USD 254.00/ha and USD 76.20/ha was attained. The GM per USD spent on chili pepper was USD 0.39 for SI and USD 0.12 for rain-fed system, whereas the GM per USD spent on okra was USD 0.16 and USD 0.06 in the respective systems of cultivation. The cost-benefit ratio (BCR) for okra was estimated at 1.16 for SI, and at 1.06 for rainfed cultivation, whereas for chilli pepper, the respective BCR values were 1.39 for SI and 1.12 for rainfed system. In conclusion, SI provided higher revenues, resulting in a gross margin capable of covering production costs and leaving a significant profit margin compared to the rain-fed system. Therefore, farmers in regions experiencing drought periods are advised to use SI along with appropriate management practices to increase crop productivity.