Movement of nitrate-N and transformations of urea-N under field conditions

Publisher Website
Google Scholar
Abstract
Summer and winter NaNO3 treatments at 400 kg N/ha were given to ryegrass [Lolium perenne] pasture on Horotiu sandy loam. The movement and adsorption of nitrate were studied under natural precipitation and ground water flow. Movement of nitrate to depths of 400 mm could be explained by miscible displacement when the soil was near field capacity, and movement was faster under unsaturated flow conditions. Adsorption measurements showed that the soil had an anion exchange capacity of 0.85 meg/100 g in 0.025 M CaCl2. These positively charged sites were able to retard nitrate movement below 400 mm. Simulated urine treatments were also made at 2 mo. intervals studied. Hydrolysis of urea was complete in 2 days in summer and 3 days in winter. Nitrification was not appreciable until after 7 days in all seasons. At soil temperatures of 7.5-10.degree. C nitrification continued to be slow and was not complete until 60 days, but at temperatures above 15.degree. C it was rapid, once initiated, and was complete in 30 days. Apparent volatilization losses of ammonia of 20-37% were recorded, rate of application having the main effect. Leaching of nitrate from under NaNO3 or simulated urine treatments was accompanied by substantial Mg movement.