Time of availability influences mixed-nitrogen-induced increases in growth and yield of wheat 1

spring wheat (Triticum aestivum)plants produce higher grain yields, more tillers, and increased dry matter when continuously supplied with mixtures of NO3 and NH4 than when supplied with only NO3. The objective of this study was to determine if mixed N needs to be available before or after flowering, or continuously, in order to elicit increases in growth and yield of wheat. During vegetative development, plants of the cultivar 'Marshal’ were grown in one of two nutrient solutions containing either a 100/0 or 50/50 mixture of NO3 to NH4 and, after flowering, half the plants were switched to the other solution. At physiological maturity, plants were harvested, separated into leaves, stems, roots, and grain and the dry matter and N concentration of each part determined. Yield components and the number of productive tillers were also determined. Availability of mixed N at either growth stage increased grain yield over plants receiving continuous NO3, but the increase was twice as large when the mixture was present during vegetative growth. When the N mixture was available only during vegetative growth the yield increase was similar to that obtained with continuous mixed N. “The yield increases obtained with mixed N were the result of enhanced tillering and the production of more total biomass. Although plants Previous studies have indicated that under hydroponic conditions,.