. 2001. Ammonia volatilization from soils fertilized with urea and varying rates of urease inhibitor NBPT. Can. J. Soil Sci. 81: 239-246. Loss of N as ammonia (NH 3 ) from surface-applied urea fertilizer may be high if hydrolysis takes place at the soil surface. The urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) may reduce NH 3 loss from urea by delaying hydrolysis. Field studies using surface chambers were conducted in 1996 and 1997 to compare the amount of NH 3 volatilized from surface applications of granular urea (100 kg N ha -1 ) treated with varying concentrations of NBPT (0, 0.05, 0.10 and 0.15% NBPT wt/wt). The studies were conducted on two Orthic Black Chernozemic soils, a Stockton fine sandy loam and a Newdale clay loam, in May and again in July to determine the relative influence of soil texture and temperature on NBPT performance at the varying rates. Ammonia losses were measured at various times to 12 d after fertilization (DAF) in 1996 and to 21 DAF in 1997. Total NH 3 losses decreased in the order of 0% > 0.05% > 0.15% ≥ 0.10% where use of NBPT reduced total NH 3 loss by 28-88% over the entire study duration, and by 82 to 96% during periods of peak loss from unamended urea. Ammonia volatilization losses from NBPT-amended urea treatments were lower in May than in July. The total loss measured at all rates of NBPT was higher for the fine sandy loam soil except in May 1997 where cool conditions resulted in slightly lower loss than for the clay loam soil. Amending urea with NBPT at a rate as low as 0.05% wt/wt can reduce NH 3 loss from surface-placed urea fertilizer, so that a greater proportion of fertilizer N is retained in the soil for plant use. The inhibitor helps reduce the amount of NH 3 derived from urea entering the atmosphere to react or to be deposited elsewhere, and may lessen the need to overfertilize to compensate for potential NH 3 losses. Le N-(n-butyl)-triamide de l'acide thiophosphorique (NBPT) est un inhibiteur de l'uréase et pourrait réduire les pertes de NH 3 de l'urée en retardant l'hydrolyse. En 1996 et 1997, les auteurs ont effectué des études sur le terrain au moyen de chambres de surface en vue de comparer la quantité de NH 3 qui s'échappe dans l'air consécutivement à l'application d'urée granulaire (100 kg N ha -1 ) renfermant une quantité variable de NBPT (0, 0,05, 0,10 et 0,15 % en poids). Les essais se sont effectués sur deux tchernozems orthiques noirs, soit un fin loam sablonneux Stockton et un loam argileux Newdale, en mai puis en juillet, et devaient préciser l'influence relative de la texture et de la température du sol sur l'efficacité du NBPT aux concentrations à l'étude. Les auteurs ont mesuré la perte d'ammoniac à divers moments jusqu'à 12 jours après la fertilisation (JAF) en 1996 et 21 JAF en 1997. La perte totale de NH 3 diminue dans la séquence 0 % > 0,05 % > 0,15 % ≥ 0,10 %, et l'addition de NBPT a réduit la perte totale de NH 3 de 28 à 88 % pendant la durée de l'étude et de 82 à 96 % lors des périodes où les pertes de l'urée non traitées étaien...

. 2000. Uptake of foliar or soil application of 15 N-labelled urea solution at anthesis and its affect on wheat grain yield and protein. Can. J. Plant Sci. 80: 331-334. Two growth chamber experiments were conducted to determine the effect of 15 N-labelled urea solution foliar-or soil-applied at anthesis on recovery of fertilizer N in grain, grain protein and grain yield of Canadian Western Red Spring wheat (Triticum aestivum L.). Recovery of 15 N-labelled urea-N in grain ranged from 4.5 to 26.7% with foliar application, and from 32.3 to 70.1% with soil application. Amending the urea solution with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) improved recovery of soil-applied N in exp. 1 only and did not increase N recovery from foliar applications. Nitrogen recovery of foliar-applied urea was increased on average from 10.6 to 25.0% by adding nonyl phenol ethoxylates (NPE), a non-ionic surfactant, to the urea solution. Grain protein was higher when urea was applied to the soil than when applied to the foliage. Addition of N at planting increased both grain protein and yield while only protein was enhanced with fertilizer N applied at anthesis. Although wheat cultivar, soil type and growing environment differed in the two experiments, protein content consistently increased with N application at anthesis, indicating the effect of N applied at anthesis is constant across a range of conditions. En revanche, le taux de récupération du N de pulvérisations foliaires passait de 10,6 à 25% quand l'urée était additionnée du surfactant non ionique NPE (nonyl phénol éthoxylates). La teneur en protéine du grain était plus élevée quand l'urée était utilisée en épandage au sol plutôt qu'en pulvérisations foliaires. L'apport de N ou semis produisait une augmentation du rendement grainier et de la teneur en protéine, alors que son apport lors de l'anthèse n'augmentait que la teneur en protéine seulement. Même si le cultivar, le type de sol et le milieu de culture n'étaient pas les mêmes dans les deux expériences, la teneur en protéine était régulièrement plus élevée à la suite d'épandage de N à l'anthèse, ce qui montre que l'effet de l'apport de N à ce stade est constant dans un large écart de conditions de cultures.