NITROGEN AND PHOSPHORUS EFFECT ON AMERICAN CRANBERRY GROWTH, YIELD AND MINERAL ELEMENT COMPOSITION

The industrial cultivation of American cranberry (Vaccinium macrocarpon Aiton) in Latvia was started during last 20 years with total plantings of more than 125 ha today. As a native wetland plant, commonly cranberries grows on poor, acid soils and are characterized as nutrients low requiring crop, however, balanced plant nutrition is vitally important to realize the full potential of cranberries as crop, to ensure adequate growth and yield production. Previous results obtained by authors from different cranberry producing plantings in Latvia frequently showed inadequate cranberry tissue supply with N and P. A field trial were established to examine the impact of N and P fertilizer rates on cranberry yield, fruit quality, morphological factors, and mineral element supply. Field experiments on cranberry cultivar 'Bergman' were conducted during 2019 cropping season in a commercial plantation established on an excavated peat bog in Latvia. The cranberries received five levels of N (0 to 40 kg N ha^-1) and P (0 to 30 kg P ha^-1) as well as N and P treatment combinations applied in spring. Cranberry leaf analyses and soil (peat) testing were used as a diagnostics tool to reveal nutrient (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, Mo, B), soil pH and EC status. In general, crop characters were significantly influenced by different levels of N and P. As expected, the results showed that combined N and P treatments with the highest rates: N30/P20 and N40/P30 resulted in the highest yields and yield parameters, as well as ensured optimal N and P concentrations in cranberry tissues. It should be noted that the rates of applied fertilizers were environmentally safe as the nutrient concentrations recommended for peat growing medium were not exceeded.