Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Plants, Soils, and Climate

Department name when degree awarded

Plants, Soils, and Biometeorology

Committee Chair(s)

Bruce Bugbee


Bruce Bugbee


William J. Doucette


Paul Grossl


Rich Koenig


The long-term effects of low and high NH4+/ NO3- uptake ratios in a system with rigorous control of pH and nitrogen concentration are poorly understood. In two replicate studies, two cultivars of wheat (Triticum aestivum) were grown to maturity with three NH4+/ NO3- ratios in hydroponic solution: 0/100, 25/75, and 85/15%. Nitrogen was controlled at ample levels throughout the 70-d life cycle and pH was controlled at 5.8 ± 0.2. An equimolar ratio of NH4+ to Cl- was used to facilitate charge balance. Nitrogen consumption and transpiration were measured daily. Flag leaves were analyzed at 10-d intervals for total nitrogen, NO3--N, and essential elements. Essential nutrient elements in the biomass and seeds were measured at harvest. Yield components , nitrogen recovery, and nitrogen assimilation were calculated. There was no difference between the NO3- only (0/100) and the low NH4+ (25/75) treatments . The high NH4+ treatment (85/15) did not reduce vegetative biomass, but decreased seed yield and harvest index by 20%. The decrease was associated with a 23% reduction in seed number head-1. The high NH4+ treatment increased percent root mass by 50% and percent sterile heads by 800%, but increased assimilated N in the seeds by 30% and in the biomass by 130%. Supplemental additions of K were effective in preventing the reduction of K concentration in the wheat tissues typically caused by high NH4+, but the high NH4+ treatment decreased the concentrations of Ca, Mn, and Zn, and increased the concentrations of S, P, Fe, and B in the wheat tissue . The uptake of Mg and Cu was similar among all three treatments. Chloride concentrations in the flag leaves increased from 0.8% in the NO3- only treatment to 2.0% in the two NH4+ treatments. This research indicates that hydroponic wheat can be grown to maturity with high levels of NH4+ with a small reduction in grain yield.