Soybean seed coating with Rhizobium inoculum is a conventional, yet expensive, practice that may result in seed damage and reduced productivity. To address these issues, in this study we developed and installed a spraying novel system on row planters that directly sprays the inoculum solution onto the seeds and furrows. We optimized the system by using the response surface methodology and a central composite design with 20 tests to evaluate the effects of the forward speed, flow rate, and spraying angle on the seed coverage. Our results show that all three variables have significant effects on seed coverage, and we obtained maximum and average seed coverages of 95.38% (experimental) or 96% (predicted), respectively. We developed a quadratic model that accurately predicts the seed coverage as a function of the forward speed, flow rate, and spraying angle, achieving a coefficient of determination of 97.24%. The optimal settings for the best seed coverage were determined to be a forward speed of 4.65 km/h, a nozzle flow rate of 400 mL/min, and a nozzle angle of 46°. Our study presents a practical and cost-effective solution for improving soybean seed coverage and enhancing crop productivity.

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