IRRIGATION AND NITROGEN MANAGEMENT TO IMPROVE
NITROGEN FERTILIZER EFFICIENCY
J.C. Stark, I.R. McCann, D.T. Westermann, and T.A. Tindall
Nitrogen fertilizer recommendations for potatoes in Idaho are based on a number of factors including
a realistic yield goal, the type and amount of crop residues incorporated into the soil, N carryover from
the preceding crop and an estimate of N mineralization. Mismanagement of N fertilizer can significantly
reduce yield and quality. Inadequate N can reduce yields by promoting early senescence and shortening
the tuber bulking period. On the other hand, excessive N levels in the soil at or before tuber set can delay
tuber growth which also shortens the tuber bulking period and reduces yield. Excessive N can also reduce
specific gravity and delay maturity, particularly when N is applied late in the growing season.
Split N applications usually increase N fertilizer use efficiency compared to single preplant applications
(Kleinkopf and Westermann, 1987). This involves applying reduced amounts of N at planting and then
providing the remainder of the crop’s N requirement by applying N fertilizer with the irrigation water.
Petiole testing should be used to adjust the amount and timing of split N applications according to crop
needs. Research and grower experience has shown that the proper use of split N applications can optimize
potato yield and quality by encouraging earlier tuber growth and maintaining maximum tuber bulking
rates until vine kill.
Applying fertilizer N closer to the time the plant actually removes it from the soil also improves fertilizer
use efficiency by reducing the potential for nitrate leaching. Studies have shown that the total amount of
N fertilizer used may be decreased by 20% by using timely split N applications. Deficiencies of other
nutrients can also reduce N fertilizer efficiency.
Irrigation management is also very important in the production of a profitable, high-quality p