Assistant Professor University of Idaho Aberdeen, Idaho
Variability in nitrogen (N) costs, environmental demand to optimize application rates, and the ongoing need to optimize nitrogen management for new and old varieties to maintain high yields and improve the quality of potatoes for the processing and fresh industries are driving factors behind this research to determine whether reduced N rates and distributed N applications could improve French fry color. Teton Russet was grown in Aberdeen, Idaho under four N rates (0, 73, 91, and 109 kg/acre) using two schedules: weekly and bi-weekly with 50% applied during vegetative growth, 25% at tuber initiation, and 25% during tuber bulking. N fertilizer was applied between 100% crop emergence [35 days after planting (DAP)] and 96 DAP with vines being terminated at 115 DAP, resulting in an 89-day growing season. Fry color was assessed every other month during a 243-day storage period at 8.9°C, using a Photovolt reflectometer, where higher reflectance values indicated lighter fry color. Improvements in fry color were observed with 91 kg/acre applied weekly and 109 kg/acre applied bi-weekly. The 73 kg/acre rate showed no difference between application schedules. Weekly application of 91 kg/acre produced fries 4.6% lighter than the same rate applied bi-weekly. Increasing the N rate to 109 kg/acre with bi-weekly application resulted in fries 3.7% lighter than those from the 91 kg/acre bi-weekly treatment. All N rates and application schedules exhibited a gradual darkening of fry color over time, with a similar pattern observed across treatments. Notably, bi-weekly applications at 91 kg/acre generally produced darker fries than weekly applications throughout the storage period. All treatments resulted in darker fries during the first 60 days, followed by stabilization over the next 90 days. These findings suggest that while reducing N rates can improve fry color, the benefits are influenced by both application schedule and storage duration.
