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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 30, 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 the 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.

Little information is available regarding N management of inbred maize (Zea mays L.), which exports less N than hybrid maize. Nitrate contamination of the groundwater has been a concern in St Joseph County in southwest Michigan where >20 000 ha of seed maize are grown on sand and sandy loam soils. Over application of N fertilizer potentially reduces profits of the local growers and poses a threat to the environment. A field experiment was conducted from 1990 to 1994 to estimate N fertilizer requirements of three different inbred varieties for maximizing yields while minimizing ground water pollution. Yield and N content of grain and stover were analyzed at the end of each growing season. Nitrate leaching was monitored throughout the 5 yr of study by collecting and analyzing drainage flows out of five large field lysimeters. Grain yield was the least responsive to N fertilization, compared with stover biomass, and grain and stover N concentrations. Analyses of yield, NO3‐N leaching and soil N balance indicated that the appropriate fertilization of the P38 mid‐season inbred approximated 108 kg N ha−1. Nitrate leaching out of unfertilized plots reached a threshold of 12 to 15 kg N ha−1 yr−1, during the last 2 yr of treatment. Application of 101 and 202 kg N ha−1 generated an average annual loss of 26 and 60 kg N ha−1, respectively, during the last 2 yr of treatment.

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