THE EFFECTS OF TILLAGE AND UREASE INHIBITORS ON NITROGEN TRANSFORMATIONS IN SOIL (BALANCE, PHOSPHOROAMIDES, AMMONIA, VOLATILIZATION)
Abstract
Research has shown that surface applications of nitrogenous fertilizers on no-till (NT) corn generally result in crop yields lower than similar application rates on conventional till (CT) corn. Since urea is a common N fertilizer, two field studies were conducted (1982 and 1983) to characterize urea hydrolysis, nitrification, denitrification, immobilization and nitrate leaching in NT and CT systems. Research has also indicated that urease inhibitors may improve the efficiency of surface-applied, urea-based fertilizers. A field study was established to study the effects of six phosphoroamide urease inhibitors on urea hydrolysis, NH(,3) volatilization, and other N transformations from urea N applied to the soil surface in NT and CT systems. Following a surface application of urea-ammonium nitrate urea, (NH(,4))(,2)SO(,4) and Ca(NO(,3))(,2) the inorganic and organic N fractions contained 50% and 10%, respectively, of the N applied to both the NT and CT systems in 1982, indicating that tillage and N source had a minimal affect on N lost through denitrification, leaching and NH(,3) volatilization. Tillage also had no apparent affect on the rate of urea hydrolysis. Incorporation of several fertilizers resulted in 20 to 40% greater inorganic N recovery than when applied to the soil surface. In contrast, the 1983 study showed that urea hydrolysis was 2.3 to 3 times faster and NH(,3) volatilization losses were 60 to 80% greater on NT than on CT soils. Recovery of inorganic N was 17 to 77% greater on CT than on NT and was attributed to significantly higher nitrification rates on NT with subsequent leaching and/or denitrification of NO(,3)('-). Studies in 1982 and 1983 showed that approximately 10% of the fertilizer N applied was immobilized for NT and CT systems. Phenylphosphorodiamidate (PPD) was the most effect of the urease inhibitors tested. Addition of PPD resulted in a 60 to 70% inhibition of urea hydrolysis and a concomitant 46 to 90% reduction in NH(,3) volatilization losses on NT and CT soils. Addition of the urease inhibitors to fallow plots, however, did not significantly increase recovery of fertilizer N in the soil profile or alter immobilization of urea N.
Degree
Ph.D.
Subject Area
Agronomy
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