Alternative systems for cultivating and side dressing specialty crops for improved nitrogen use efficiency

In Arizona raised bed vegetable crop production, crops are conventionally cultivated and fertilized post-emergence using tools positioned close to the plant row. These practices can injure plants through excessive soil disturbance and by pruning sensitive feeder roots. Furthermore, conventional side-dress applicators place fertilizer at the edge of bed sidewalls, a location that is not optimal for plant uptake. The goal of this project was to determine if alternative technologies and systems for cultivating and side-dressing that induce minimal soil disturbance and more optimally place fertilizer reduce fertilizer inputs and increase yields in vegetable crops. Field trials with iceberg lettuce, romaine lettuce and broccoli were conducted to compare these alternative systems with conventional methods. Results showed that use of an alternative, point injection fertilizer applicator which placed fertilizer in the root zone increased nutrient uptake efficiency by over 20% and crop yield by 19% in iceberg lettuce when deficient rates of nitrogen were applied. Although nutrient uptake was not improved by using the point injection applicator in romaine lettuce, there was a trend that crop yields were increased by approximately 11% when the device was used and bed sidewalls were shaved (conventional cultivation). Yield improvements were not realized when the point injection applicator was used in conjunction with a cultivating technique that left bed sidewalls intact. This result was not expected since it was hypothesized that bed shaving would prune roots which would limit nutrient uptake, crop growth and yield. In broccoli, use of the point injection in conjunction with cultivation techniques that either shaved sidewalls or left them intact increased nitrogen uptake by more than 27% as compared to the standard applicator. Although not statistically significant, total yield and marketable yields were also higher by >8% and >15% respectively when the beds were not shaved and point injection applicator was used. Combined, the study results imply that fertilizer applicator and cultivation systems that place fertilizer in the root zone and induce minimal soil disturbance improve nutrient use efficiency and/or increase yield in lettuce and broccoli production. Additional trials at the research and field scale levels are needed to confirm this finding.