Presidedressing Soil Nitrate Testing (PSNT) Effective in Reducing N Fertilizer Use in Vegetable Production
The utility of PSNT in determining N sidedress requirement of cool-season vegetables (broccoli, cauliflower, celery and lettuce) was evaluated in a total of 20 trials conducted in commercial fields in California in 1996–97. Fields were selected which had soil NO3-N concentration >20 mg·kg-1 at the time the cooperating grower made the first sidedress N application. The grower's fertility program was compared with two reduced N treatments, established by skipping either the first, or the first and second, sidedress N application. There were four replications of each N treatment, in a randomized block design. All fields were conventionally irrigated (sprinkler and/or furrow). Crop and soil N status was evaluated throughout the season. No yield or quality differences were observed in any field by skipping the first N sidedress; in only three fields was yield reduced by skipping two sidedress applications. Total crop N uptake varied little among N treatments in most fields, despite differences in seasonal N application of as much as 200 kg·ha–1. These results indicate that PSNT can reliably identify fields in which sidedress N application can be delayed or eliminated. A soil NO3-N “quick test” was evaluated and proved to be a practical on-farm method to determine soil NO3-N status.