Effects of nitrogen fertilization on fruit yield and quality of processing tomatoes

Four processing tomato Lycopersicon esculentum Mill.) cultivars (CC337, H9230, H9492 and H9553) were field-grown in southwestem Ontario using five N fertilization rates in each of 4 yr (0, 50, 100, 150 and 200 kg N ha(-1) in 1999 and 0, 100, 150, 200 and 250 kg N ha(-1) in 2000, 2001 and 2002). Total fruit yield increased linearly as N rate was increased except in 2001, which was a dry year. Responses of marketable yield to fertilizer N rate were dependent on cultivar and the year. In years when sufficient soil water was available, N fertilizer rates of 200 kg ha(-1) or higher were required to produce the maximum marketable yield for the four cultivars. In the dryer years, the response to fertilizer N rate was cultivar dependent, and the application of 150 to 200 kg N ha(-1) was sufficient to maximize marketable yield. Fertilizer N above the rate required for maximum marketable yield increased green fruit yield at harvest. Nitrogen rate did not affect the soluble solids (SS) content, firmness, size or colour of marketable fruit. Differences in yield and fruit quality were noted among cultivars. H9553 was the highest-yielding cultivar. H9230 had the largest fruit size. CC337 generally had the best red fruit colour and the lowest percent SS. H9492 generally had the highest percent SS. To attain maximum marketable yields, it appears that N rates should be adjusted based on cultivars, anticipated rainfall levels and availability of irrigation.