ASGSB 1999 Annual Meeting Abstracts

NITROGEN DYNAMICS IN ADVANCED LIFE SUPPORT: GROWING WHEAT WITH 80% AMMONIUM. D.J. Muhlestein, T. Hooten, J.M. Norton, and B. Bugbee. Plants, Soils & Biometeorology Dept., Utah State Univ., Logan, UT.

Conversion of NH₄⁺ to NO₃^- in advanced life support systems can be difficult. The ability to supply NH₄⁺ directly to the plants can eliminate the need for a nitrifying bioreactor. Many plant physiology textbooks indicate that NH₄⁺ is toxic to plants, but we now know that this may not be true if pH is rigorously controlled. However the long term effects of high NH₄⁺/NO₃^- uptake ratios are poorly understood. In four studies, two cultivars of wheat were grown to maturity with NH₄⁺/NO₃^- ratios from 0 to 0.85 in recirculating hydroponic solution. In the third and fourth studies, NH₄⁺ was supplied as either (NH₄)₂SO₄, NH₄Cl or both. Contrary to conventional wisdom, there was no beneficial effect of supplying 25% of the N as NH₄⁺ compared to a nitrate control. The high NH₄⁺ treatment (85% NH₄⁺) reduced seed yield by 20% in the first two studies, but yield was not reduced in the third and fourth studies. Chloride and sulfate were equally effective as counterbalancing ions for NH₄⁺. Nitrification potential was measured in the fourth study to estimate NH₄⁺ conversion to NO₃^-. Potential nitrification could account for a maximum of only 0.2% of N in plants taken up over the entire life cycle. Studies are currently being conducted using inoculation and at pH 5.8 and 7.0 to quantify the potential for nitrification in NH₄⁺-based hydroponic solutions.

Back to Meeting Program