Influence of cultivar, microbiological fertilizers and growing seasons on nitrate content in lettuce

Lettuce belongs to a group of leafy vegetable crops with special importance in human nutrition. Along with healthy compounds lettuce can accumulate nitrate in leaves. The purpose of this study was to examine the effects of genotype, microbiological fertilizers and season on plant weight and nitrate content in outer and inner leaves. Green cultivars (′Kiribati′, ′Aquino′, ′Aleppo′) were cultivated in a fertile soil, in a greenhouse trial at the company Iceberg Salat Centar, during three successive seasons (autumn, winter and spring). Microbiological fertilizers (EM Aktiv, Vital Tricho and combination of EM Aktiv and Vital Tricho) were applied in the soil before trials and foliar. In spring cultivar ′Aquino′ showed the highest head fresh weight (360.3 g). All microbiological fertilizers led to increased head fresh weight in ′Aquino′ during autumn trial. Mainly fresh weight was higher in spring and winter compared to autumn. Cultivar ′Aquino′ showed the highest nitrate content (985.4 mg/kg, autumn) in outer leaves with application of Vital Tricho. Opposite to that, the lowest nitrate content was found in inner leaves of cultivar ′Aleppo′ (35.4 mg/kg, spring) with combination of fertilizers. Generally, microbiological fertilizers significantly increased nitrate content in outer and decreased in inner leaves. In both leaves the lowest nitrate level was measured in spring season. During all trials nitrate content remained under allowed level of European Commission Regulation (563/2002) for protected lettuce