Abstract
The effectiveness of ammonium nitrate, ammonium sulfate, calcium nitrate and urea for winter grown head lettuce (Lactuca sativa L.) was evaluated. N source did not affect yield, quality factors, head size or total N accumulation. Applications of fertilizers containing NO3-N resulted in slightly higher NO3-N concentrations in the midribs. Plant growth and N accumulation were similar with all N sources at low temperatures. Air temperature below 13°C for a week or more sharply reduced N uptake and plant growth with all sources. About 80% of the total N is taken up by the plants in the 4 weeks before harvest. N source did not affect quality.

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