NITROGEN AND POTASSIUM FERTILIZATION OF POTATOES - EVALUATING NUTRIENT ELEMENT INTERACTIONS IN PETIOLES WITH RESPONSE SURFACES

We studied the effects of fertilizer N and K rates on the nutrient con centrations in petioles of Russet Burbank potato grown on a low-K, low -Cl, highly calcareous Millville silt loam soil. Phosphate and CaSO4 w ere applied uniformly so that P and S did not limit plant growth. An i ncomplete factorial experimental design, utilizing 14 combinations of fertilizer N and K, including two forms of Y, was used to develop a mu lti-dimensional regression model. This model was then used to produce response surfaces as an aid to analysis of the results and to illustra te the fertilizer treatment effects and their interactions on petiole chemistries. Nitrogen, K and Cl fertilizers had complex effects on pet iole concentrations of NO3-N, SO4-S, Cl, K, Ca and Mg. Nitrate-N and C l were mutually antagonistic. Soil N had a large positive effect on pe tiole K and Mg levels and, to a lesser extent, petiole Ca levels. Ther e was competition between K and Mg in petiole concentration. The sum o f K, Ca and Mg was essentially constant across fertilizer treatments a nd sampling times. The sum of NO3-N, SO4-S and Cl was highly variable. The ratio of cations to anions ranged between three and five across f ertilizer treatments and sampling times. The data indicate that calibr ation of the major nutrient element concentrations in potato petioles, as a guide to fertilization, requires knowledge of background soil fe rtility conditions with respect to N, K, Cl, Ca and Mg, and an underst anding of the antagonisms and synergisms among these elements.