The objective of the experiment was to determine the effect of nutrients (different doses of chlorine, sulphates and calcium as well as different forms of nitrogen fertilizers: Ca(NO3)2 + NH4NO3, NH4NO3, NH4NO3 + CaCl2, NaNO3) on yield and content of N-NO3, Nog., P, K, Ca, Mg and Na in butter lettuce (Lactuca sativa L.) cv. Vilmorin. A pot experiment with four replications was repeated three times in 2007 (from 30th January and from 30th March) and in 2008 (from 31st March). It was established in the ‘Plant House’ of the Chair of Agricultural Chemistry and Environmental Protection UWM in Olsztyn. Lettuce seedlings were planted into pots containing 2 dm3 substratum. Nitrogen was applied three times, every 10 days, each dose consisting of 100 mg N.dm-3 of substratum applied to soil; identical doses of phosphorus, potassium and magnesium were introduced to the substratum before planting lettuce. Irradiation period was 12 hours every day. Lettuce was harvested after 6 weeks. Determinations of Nog (Kjedahl’s method), P (vanadium- molybdenum method), K, Ca, Na (flame photometry – ESA), Mg (atomic absorption spectrophometry – ASA) were performed having wet mineralised plant samples in H2SO4. Concentration of nitrates (V) was determined in fresh matter (potentiometrically, using a ion-selective electrode) in a 0.03 mol.dm-3 CH3COOH according to NOWOSIELSKI (1988). The smallest number of lettuce heads (statistically significant) was obtained after NaNO3 fertilization. The concentration of N-NO3 declined advantageously following an NaNO3 treatment. In contrast, the highest accumulation of nitrates(V) occurred after application of lime saltpetre in conjunction with ammonium nitrate. The composition of minerals in butter lettuce cv. Vilmorin, such as phosphorus, potassium, magnesium and sodium, was more beneficially affected by fertilization with sulphate compounds (K2SO4 + MgSO4) rather than chlorine compounds (KCl + MgCl2). Soda nitre significantly depressed the content of magnesium and calcium in plants, had no effect on the concentration of phosphorus and increased accumulation of sodium and potassium.
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