EFFECT OF NITROGEN FERTILIZATION ON THE QUALITY CHARACTERISTICS OF FIVE NORTH AMERICAN AMBER DURUM WHEAT CULTIVARS

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Abstract
Five North American amber durum wheat cultivars were grown at three levels of soil fertility by applying N fertilizer (ammonium nitrate 34–0–0) at 0, 56 and 224 kg/ha. Application of 56 kg/ha of N did not increase grain yields overall, but at 224 kg/ha of N the five cultivars exhibited an average yield advantage of 7.8%. Test weight and kernel weight decreased with increasing N fertilizer, but semolina milling yield was not affected. Protein levels increased for all cultivars at each level of N fertilizer, but kernel hardness, as measured by semolina granulation, was not affected. Gluten strength and gluten protein solubility in lactic acid were not influenced by level of N fertilizer. Spaghetti pigment decreased with increased N fertilizer level due to the combined effects of decreased semolina pigment and increased pigment loss during spaghetti processing. Pasta dough farinographs exhibited decreased mixing times, increased maximum consistency and increased tolerance index with increasing N fertilizer due to increasing protein content. As N fertilizer levels increased spaghetti cooked weight decreased, solids lost to cooking water decreased, and cooked spaghetti resilience and firmness improved at both optimum cooking time and after overcooking for 10 min. All the cooking quality effects could be attributed to increased levels of protein at high N fertilization levels.