Root Growth, Nitrogen Uptake, and Tillering of Wheat Induced by Mixed‐Nitrogen Source

Abstract

Growth and yield of wheat is enhanced when plants are provided with mixtures of NO3 and NH4, compared with either form alone. The objective of this experiment was to further evaluate the effects of N form on growth and tillering of wheat, with particular attention to tiller phenology, root morphology, and N uptake. Two species of spring wheat (Triticum durum Desf. cv. Inbar and Triticum aestivum L. cv. Len) were grown in the greenhouse with five different ratios of NO3‐N and NH4‐N (100/0, 75/25, 50/50, 25/75, 0/100). Compared with either form alone, mixtures of NO3 and NH4 increased vegetative growth of both cultivars due to enhanced development of coleoptilar and higherorder tillers. The magnitude of growth enhancement was greater (=60%) for Inbar than Len. For both cultivars, growth on N mixtures increased the number, mass, and primary branching of nodal roots, but did not affect seminal root growth. However, because nodal roots per tiller and nodal root branches per tiller were unaffected by N treatment or cultivar, changes in root morphology cannot fully explain treatment‐induced differences in tillering. Although plants of both cultivars supplied with mixed N absorbed more total N, the response was larger for Inbar because of its ability to sustain NO3 uptake when external NO3 concentrations were reduced by substitution with NH4, and to more than compensate for the decrease in NO3 uptake by additional absorption of NH4. Therefore, mixed‐N‐induced increases in tillering are also related to enhanced N uptake as well as altered root growth.