Tuber Yield and French Fry Processing Quality Response of Potatoes to Nitrogen Rate

This study was performed to evaluate the effect of nitrogen (N) application rates (0, 75, 150, 225, 300 and 375 kg ha−1) on total tuber yield, marketable tuber yield, dry matter content, reducing sugar content, sucrose content and fry colour index of two potato cultivars (Kennebec and Shepody) in 2016 and 2017. Nitrogen application significantly affected the yield and processing quality of tubers. Total and marketable tuber yields responded quadratically to N application and 173–197 kg ha−1 N fertiliser application was required to achieve the maximum marketable yield for Kennebec and 232–312 kg ha−1 for Shepody based on 2-year average data. The processing quality of tubers also responded quadratically with increasing N application rate. The optimal N application rate (Nopt) required to obtain the highest quality of French-fried potatoes ranged from 98 to 200 kg ha −1 N for Kennebec and from 123 to 205 kg ha−1 for Shepody. These results indicated that the choice of N application rate requires a compromise between tuber yield and processing quality.