Total N uptake for potato crops in southern Idaho usually ranges from about 150 to 250 lb N/acre, depending on cultivar and yield potential. At harvest, about 60-65% of the total plant N is contained in the tubers, while about 30% remains in the vines. During tuber bulking, potato plants require about 2.0 to 3.0 lb N/acre/day depending on tuber growth rate.
About 60% of the seasonal N requirement is taken up by 75 days after planting. Consequently, adequate N must be available to the crop early in the season to allow for sufficient canopy development. Research shows that about 150-180 lb N/acre from soil and fertilizer sources is required by the time the rows begin to close to provide for optimum canopy development and yield. However, excessive N availability prior to tuber initiation can delay tuber bulking by up to 2-3 weeks, reducing tuber yields by as much as 80-120 cwt/acre. Excessive early-season N can also increase the susceptibility to brown center and hollow heart. Excessive late-season N applications usually reduce specific gravity and skin set, and increase the potential for nitrate leaching.