EFFECT OF AMMONIA AND ITS OXIDATION PRODUCTS ON RATE OF NITRIFICATION AND PLANT GROWTH

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Abstract
This study was made to determine the comparative nitrification of ammonia when injected into the soil and applied in irrigation water. In addition, the influence of growing plants on nitrification and the probability of formation of Corbet''s intermediates were studied. Nitrification proceeds at about the same rate in presence of barley plants as in the soil above but nitrite accumulates to a greater extent in absence of growing plants. Dry weight and nitrogen uptake of barley increase with ammonia concentration to a maximum at 260 ppm. N but decrease beyond this concentration. Nitrite has no apparent toxic effect on the plants. A nitrogen balance on ammonia-injected Gila fine sand loam incubated over a 17-day period accounted for all nitrogen added. Evidence points to the fact that hydroxylamine and hyponitrous acid do not form in the course of nitrification. These two intermediates when incorporated with the soil showed no appreciable oxidation over a 30-day period whereas nitrite was quantitatively oxidized. Presence of hydroxylamine could not be detected analytically. The high positive free energy of formation of hyponitrous acid, its weak dissociation as an acid, and its rapid decomposition into nitrous oxide and loss from the soil, lead to the conclusion that Corbet''s theory based on these intermediates is no longer tenable.