Hydrolysis of formamide and volatilization of ammonia from nitrogen fertilizers added to soils
A simple and sensitive method for the determination of formamide was developed. This method involves the colorimetric determination of the ferric-formohydroxamate complex produced upon the reaction of Fe('3+) with the formohydroxamic acid produced from the reaction of formamide with hydroxylamine under alkaline conditions. Application of the method to soil extracts obtained with 2 M KCl made 5 mM with respect to uranyl acetate showed quantitative recovery (98 to 101%) of formamide added to soils (20 to 200 (mu)g of formamide N/g of soil);The rate of hydrolysis of formamide increased with increasing temperature of incubation and organic C content of the soils. The time necessary for complete hydrolysis of formamide (1000 (mu)g formamide N/g soil) under aerobic conditions ranged from 24 to 84 hours at 10(DEGREES)C and from 8 to 20 hours at 30(DEGREES)C. The rate of hydrolysis of formamide in air-dried soils was lower than that in field-moist soils. The amounts of formamide hydrolyzed in soils treated with 1000 (mu)g of formamide N/g of soil under waterlogged conditions were less than those hydrolyzed under aerobic conditions. Addition of urea, calcium dihydrogen phosphate, monoammonium phosphate, and potassium dihydrogen phosphate reduced the rate of hydrolysis of formamide in soils;Studies on NH(,3) volatilization from various N fertilizers applied to soils (134 mg N/chamber) under laboratory conditions showed that high amounts of NH(,3) were lost in 12 days from urea (33 to 40%) and formamide (31 to 36%) when surface applied to acid and calcareous soils. Ammonia volatilization from ammonium sulfate and diammonium phosphate ranged from 35 to 53% of the N added to calcareous soils, but was lower (< 12%) in the acid soils. The presence of a crop residue cover over the soil surface greatly enhanced NH(,3) volatilization from urea (37 to 43%) and formamide (43 to 55%). Shallow incorporation of formamide, urea, and diammonium phosphate decreased but did not eliminate NH(,3) losses; still sizable amounts of NH(,3) (12 to 19%) were lost from formamide and urea. Banding the fertilizers in the soil was the most efficient way of reducing losses of N through NH(,3) volatilization. In addition to NH(,3), formamide was volatilized upon its application to soils. Formamide volatilization ranged from < 1.5% when surface applied to bare soils to 16% when applied to plant-residue-covered soils.