Ensuring nitrogen applications targeting the optimum rate is critical in tomato production. This is because nitrogen (N) requirements in tomato production may vary depending on the soil type, location, climate, and cultivation practices. Despite tomato being a major vegetable crop in MS, information on the N requirements for commercial production in the state is limited. Therefore, this study was conducted in an open field to determine the critical nitrogen rate for commercial tomato production under the northeast growing conditions of MS. The study evaluated six N application rates (0, 67, 101, 135, 202, and 269 kg ha-1) arranged in a randomized complete block design with four replicates per treatment. Red Duce variety of tomato was planted, and nitrogen was applied at 50% pre-plant (33-0-0) and 50% fertigation (15.5-0-0). Both potassium and phosphorus were the same for all treatments and applied at 100% pre-plant using 0-0-60 and 0-46-0 respectively. Preliminary results indicate that higher N application rates significantly increased total fruit yield, total marketable yield, fruit sizes, and total biomass. The highest total fruit yield (93.79 t ha-1), total marketable yield (71.58 t ha-1), large fruit yield (10.40 t ha-1), and total biomass (6.96 t ha-1) were observed at 269 kg N ha-1. Increasing N application rates significantly increased tissue N concentration. Therefore, the greater yield observed at higher N application rates was attributed to the consistently higher tissue N concentration from leaf samples collected at different weeks during the growing season. Based on the results obtained, the critical N application rate for open-field fresh-market tomato production in northeast MS could be up to 269 kg ha-1. However, follow-up studies are currently being conducted to validate these preliminary results.
