These areas should be tested and fertilized separately. To compensate for low P availability when free lime is present in the soil, rates of P are increased with increasing levels of free lime. Soil test concentrations and rates of P2O5 needed are shown in Table 2. Soil extractant for P is NaHCO3. Soil test concentrations and rates of fertilizer needed to produce potatoes are shown in Table 3.
Potassium is relatively immobile in the soil.
For best results, K fertilizers should be applied preplant and mixed into the seedbed. Banding beside the plants has been used successfully but is not as effective as K fertilizer which has been broadcast and incorporated. Potassium fertilizer applications reduce specific gravity of harvested tubers. Growers should avoid over-fertilization of potatoes with K fertilizers. When specific gravity of tubers is important, potassium sulfate is the preferred K fertilizer source.