UBC Theses and Dissertations
Evaluation of the nitrification inhibitors n-serve and atc with urea fertilizer Guthrie, Thomas Flagstad
The purpose of using chemical nitrification inhibitors is to delay the oxidation of ammoniacal fertilizers during the early part of the growing season in order to minimize N losses prior to the period of maximum crop uptake. Since NH₄⁺ is electrostatically attracted to soil particles, leaching losses would be minimized, and denitrification losses could not occur in the absence of NO₃⁻. Thus, smaller amounts of fertilizer N would be required, resulting in lower inputs of money and energy as well as less potential for environmental pollution. A study (Chapter Two) was initiated in the fall of 1977 to determine if ATC could minimize overwinter losses of fall-applied N. Urea (200 kg N/ha) with or without a 1% coating: of ATC (4-amino-l,2,4-triazole) was banded or broadcast onto a silt soil on November 8, when the soil temperature at 10 cm depth was 1.9°C. The soil was sampled to a depth of 90 cm at approximately one month intervals until April, and NH₄⁺ and NO₃⁻ were determined. In the banded plots, some nitrification occurred prior to January, but from this date unti1 March there was very little change in soil NH₄⁺ levels. Overall, from December to April, there were 70 and 48% decreases in the 0-15 cm plots without and with ATC, respectively. In all the broadcast plots, regardless of ATC treatment, nitrification proceeded steadily throughout the sampling period, with 93 and 85% decreases from the December 0-15 cm NH₄⁺ levels in the non-ATC and ATC plots, respectively. It is concluded that ATC is partially effective in minimizing N losses when applied in the fall as a band with urea, but when broadcast there is no effect on nitrification. Leaching of the water-soluble ATC was the likely cause of its poor effectiveness. Significant leaching of urea from the zone of application was also found to occur during the first month following its application. A laboratory study (Chapter Three) was conducted to determine the influence of the nitrification inhibitors ATC and N-Serve [2-chloro-6-(trichloromethyl)-pyridine] on urea hydrolysis in a silt soil at 2 and 12°C. There was no delay of ureolysis caused by the presence of these chemicals, even at 20 times the recommended application rate. At 2°C the rate of hydrolysis was about half that at 12°C, with 21 and 7 days being required for complete hydrolysis at 2 and 12°C, respectively. These results suggest that leaching of urea may occur following its application to a cold soil during periods of heavy precipitation as was found in the winter nitrification study (Chapter Two). A series of field experiments (Chapter Four) was conducted with silage corn (Zea mays L.) to compare the effectiveness of the nitrification inhibitors ATC and N-Serve in a loamy sand and a silt. Urea was coated with the inhibitors at a rate of 1% of active ingredient per weight of N and applied as a band or broadcast in the spring of 1977 and 1978. Neither inhibitor significantly affected nitrification when applied as a broadcast treatment to either soil. In the silt, both inhibitors were equally effective in delaying nitrification when banded, whereas in the loamy sand ATC was much more effective than N-Serve. The effectiveness of N-Serve persisted much longer in the silt (86 days) than in the loamy sand (23 days). This suggested that volatilization of N-Serve severely limited its effectiveness in the loamy sand. There was no significant improvement in crop yields or N content due to inhibitor treatment in either soil.
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