Abstract
Abstract Urea, ammonium nitrate (NH4NO3), and several controlled-release N (CRN) fertilizers were compared as sources of N for head lettuce (Lactuca sativa L.). CRN fertilizers varied widely in their effectiveness. Materials with the fastest N-release characteristics gave the poorest results when applied preplant. Effectiveness of some slow-release materials depended on time of application. Neither NH4NO3 nor urea were good sources when applied preplant but were effective in 3 equal 56 kg N/ha applications throughout the season. Methylene urea (MU), F2950, was most effective when applied 30 days after planting. Sulfur-coated urea (SCU), F9999, produced the most vigorous seedlings and plants with the greatest uniformity and harvestable heads with earliest maturity, best head size, and color.
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