Mixed nitrogen nutrition and productivity of wheat grown in hydroponics

The objective of this study was to study the effects of nitrogen (N) supplied as either mixtures of NO₃ and NH₄ or as all NO₃ on the final yield of spring wheat. Two separate greenhouse experiments evaluated the durum spring wheat (Triticum durum L.) cultivar 'Inbar' in 1986, and the hard red spring wheat (Triticum aestmum L.) cultivar 'Len' in 1987. Nitrogen treatments consisted of all NO, or mixtures (75/25 or 50/50) of NO₃ and NH₄. At maturity, plants were harvested, separated into leaves, stems, roots, and grain, and each part analysed for dry matter and chemical compositionCompared to plants receiving only NO₃ as the source of N, mixed N nutrition resulted in greater accumulation of whole plant reduced-N (49 to 108% more), phosphorus (38 to 69% more), and potassium (25% more) for both cultivars. In all cases, plants produced higher grain yields (28% for Len to 78% for Inbar) when grown with mixed N nutrition than with only NO₃. The yield increase was not associated with heavier grains or more grains per ear, but rather with an increase in the number of ear-bearing tillers per plant. For both cultivars, the higher yields with mixed N resulted from the production of more total biomass (36 to 76%) as the partitioning of dry matter between plant parts was not altered by N treatment. Under the hydroponic conditions of this experiment, the utilization of both NO₃ and NH₄ resulted in greater growth, nutrient absorption, and yield than NO₃ alone, which was primarily associated with an enhancement in tiller development