Nitrification Potential in Arid Western Soils

Nitrification rates were determined by perfusion method in Southern Curlew Valley (Utah) soils from 0 to 1.3 meter profiles as a function of seasons. Ammonification rates were determined at various moisture contents and seasonal variations of ammonium concentration in the same soils were estimated. Rate of nitrification was higher in warm showery periods (May and June) than in colder periods (September, October and November). In the top 3 cm layer, nitrifying activity was several fold higher than in the rest of the profile. Cultivation increased the nitrification rate. Considerable ammonium fixation by soil particles, volatilazation of ammonia and nitrite accumulation were evident. Nitrite accumulated in samples as the pH of perfusate increased above 7.8. Accumulation of nitrate had a 8-10 days lag period, which was followed by a logarithmic phase. Nitrification was inhibited by added amendments, especially by desert plant litter. Ammonium-nitrogen values in soils were between 1-105 ppm, with higher values in later fall (November) samples. Top 3 cm layers showed higher ammonium-nitrogen values than other (5-20, 40-50, 70-80, and 110-130cm) layers. Ammonification rate increased with increasing in soil moisture in casein amended soils. Moisture content did not significantly affect ammonification in litter amended soils. Volatilization of ammonia was highest at 40% water-holding capacity (W. H. C.). Volatilization decreased with increase or decrease in moisture content above or below 40% W. H. C