Response of Nooksack potatoes to nitrogen fertilizer

The Nooksack cultivar because of differing characteristics may have different responses to grower management practices developed principally for Russet Burbank. This study was conducted to determine the effects of nitrogen on yield, grade, and specific gravity of the Nooksack cultivar. In irrigated field experiments, N fertilizer was sprinkler-applied daily on Quincy sand soil. In other experiments, on a Warden silt loam soil all N was broadcast and incorporated before planting. Fertilization rate did not significantly affect tuber grade or specific gravity. Short term shifts in N supply did not cause tuber deformities and poor grades as they commonly do with Russet Burbank. Nooksack, while responsive, did not have a strong positive response to N fertilization. Tuber yields were depressed at fertilizer plus residual N levels above 200 kg/ha on Warden silt loam and above 300 kg/ha on Quincy sand. This difference was because of variation in NO₃ leaching and soil N mineralization and was reflected in calculation of optimum N rates. Nooksack may require less N fertilization than Russet Burbank partially because of the strong dormancy of Nooksack tubers that retards emergence and shortens growing season. Management to promote more rapid dormancy break and lower N nutrition during tuber initiation could result in earlier establishment, earlier tuber bulking, and greater yields of Nooksacks.