EFFECT OF COMPLEX FERTILIZERS USED IN EARLY CROP POTATO CULTURE ON LOAMY SAND SOIL

To obtain a high tuber yield of early crop potato good conditions for plant growth must be ensured. Potato has a relatively shallow root system and requires significant nutrient inputs to maintain tuber productivity and quality. The paper presents the results of the research on the effect of complex fertilizers type NPK MgS with and without microelements from the nitrophoska (HydroComplex, Nitrophoska Blue Special and Viking 13) and the amophoska group (Polimag S), and single-nutrient fertilizers on the plant growth and tuber yield of very early potato cultivars (‘Aster’, ‘Fresco’, ‘Gloria’) on loamy sand soil. The field experiment was carried out in mideastern Poland (52°03'N, 22°33'E). Potatoes were harvested 75 days after planting (the end of June). The type of fertilizer (single-nutrient or complex fertilizer) slightly affected the growth of potato plants. With the use of complex fertilizers, the assimilation leaf area and leaf area index (LAI) were similar to the application of single-nutrient fertilizers. Of the examined complex fertilizers, Viking 13 (representing the nitrophoska group without microelements) resulted in a smaller increase of assimilation leaf area in comparison with the cultivation without mineral fertilization. The type of fertilizer exerted a greater influence on the plant growth of ‘Aster’ (Poland) than ‘Fresco’ (The Netherlands) and ‘Gloria’ (Germany). The productive effects of complex fertilizers in early crop potato culture on loamy sand soil were comparable with single-nutrient fertilizers. The highest tuber yield was achieved with the application of Nitrophoska Blue Special (from the nitrophoska group with the lowest NNH4+ concentration); the total tuber yield was higher on average by 2.94 t*ha-1 (21.0%) and the yield of marketable tuber fraction (diameter above 30 mm) by 2.55 t*ha-1 (20.4%) in comparison with the cultivation without mineral fertilization. Although the total tuber yield was a little lower, the share of large tubers (diameter above 51 mm) in the yield was recorded with the use of Polimag S (from the amophoska group and with the most Mg, S, Zn and B concentration of all complex fertilizers applied) and Viking 13 (from the nitrophoska group with Ca). The single-nutrient and complex fertilizers applied in the experiment had no effect on the dry matter, starch or Lascorbic acid content in potato tubers. Regardless of the type of fertilizer applied, the tuber yield, average weight of one tuber and the share of medium-sized tubers (diameter of 4150 mm) in the yield of ‘Aster’ were highest. The yield of marketable tuber fraction of the ‘Aster’ was higher than ‘Fresco’ and ‘Gloria’ on average by 3.03 t*ha-1 (22.0%) and 4.57 t*ha-1 (37.4%), respectively. About 25% of the ‘Gloria’ yield made up of non-marketable tubers (diameter below 30 mm). Tubers of ‘Aster’ contained more dry matter and starch than ‘Fresco’ and ‘Gloria’, however, the content of Lascorbic acid in tubers of the tested potato cultivars was similar.