Nitrogen fertilizer efficiencies on potatoes

Nitrogen fertilizer efficiencies must be known to successfully apply N fertilizer according to crop growth needs. The objective of this study was to determine the recovery, partitioning, and translocation of N fertilizer applied at different times for potato production. Russet Burbank potatoes were fertilized preplant with¹⁵N-depleted ammonium sulfate, and during early and late tuber growth with urea containing K¹⁵NO₃ in 1978 or (¹⁵NH₂)₂CO in 1980. All N applications increased tuber yields above the control treatments. The N recovery efficiency was 60% for the preplant N application, and over 80% and near 60% for the N applications during tuber growth in 1978 and 1980, respectively. Good agreement was found between the isotope and difference methods of determining N recovery efficiencies. Labeled N was initially concentrated in the stems and leaves, particularly if applied during tuber growth. Over 80% of the assimilated, labeled nitrogen was found in the tubers at the start of plant maturation. These data indicate that a significant improvement in N fertilizer efficiency would result from split N fertilizer applications made according to crop growth needs.