Effects of nitrogen application before sowing, compared with effects of split applications before and after sowing, for irrigated wheat on the Darling Downs.

Abstract

On a nitrogen (N) deficient soil on the Darling Downs, yield of irrigated wheat was increased by the application of N as anhydrous ammonia at rates up to 150 kg/ha before sowing. Nitrogen applied at 150 kg/ha before sowing did not increase grain protein concentrations, 300 or 400 kg/ha of N being needed. Nitrogen applications before sowing and during tillering were usually more effective in promoting yield than dressings applied after tillering or applied as several suboptimal dressings between tillering and flowering. Tillering was enhanced by N applied either before sowing or during tillering, whereas application after tillering increased grain size and protein concentration in the grain. Split applications involving equal quantities of N applied to soil before sowing as anhydrous ammonia and to the foliage at tillering as urea solution produced similar grain yields as when the same amount of N was applied before sowing as anhydrous ammonia. Similarly split applications, when equal quantities of N were applied before sowing and after sowing at tillering and boot, were as productive as where all the N was applied before sowing. All urea foliar sprays caused leaf burning, which became evident the day after application. Split N applications were as effective as one application before sowing in increasing the quantity of N contained in grain and generally more effective in increasing the quantity of N in straw. Splitting the N application invariably increased grain protein concentration, and this would seem its chief advantage for irrigated wheat over applying all the N before sowing.