Durum grain quality as affected by nitrogen fertilization near anthesis and irrigation during grain fill

Nitrogen fertilization and irrigation practices can affect durum [Triticum turgidum subsp. durum (Desf.) Husn.] grain quality, especially protein content. The purpose of this study was to determine if irrigation frequency during grain fill influences the effectiveness of N applied near anthesis in increasing durum grain quality. A field study was conducted at Maricopa, AZ on a Casa Grande sandy loam soil (fine-loamy, mixed, superactive, hyperthermic, Typic Natrargid). Durum was grown with recommended amounts of N fertilizer until anthesis when 0, 3.4, and 6.7 g N m^-2 were applied and irrigation based on 39, 50, and 70% depletion of plant-available soil water was initiated, irrigation during grain fill had no effect on grain yield or grain quality except in 1996, when irrigating at 30, 50, and 70% depletion resulted in hard vitreous amber counts (HVAC) of 813, 870, and 934 g kg^-1, respectively. Nitrogen application near anthesis of 0, 3.4, and 6.7 g N m^-2 resulted in grain protein contents of 115, 127, and 140 g kg^-1 in 1995 and 132, 141, and 151 g kg^-1 in 1996, respectively. Nitrogen application near anthesis increased grain protein yield and HVAC in both years of rite study and increased grain yield, grain volume weight, and kernel size in 1995. The results of this study suggest that N fertilizer application near anthesis has a primary influence on durum quality and that effects of irrigation frequency during grain fill are inconsistent or relatively minor.