Influence of urease and nitrification inhibitors on ammonium and nitrate supply and the soil microbial population in western Canadian soils
Improving nitrogen use efficiency and limiting losses of N from the soil system is important both economically and environmentally. This study assessed the potential of using a urease inhibitor, Agrotain®, or a nitrification inhibitor, nitrapyrin, to create a slow release effect similar to that found in sulfur coated urea in western Canadian soils of the Brown and Black soil zones. The nitrapyrin significantly reduced the cumulative NO3- supply to the point of inhibition of nitrification for 21d in the Brown soil, but had little effect on the Black soil. Nitrapyrin had little effect on the supply of NH4+ in both soils. The Agrotain® had some effect on NO3- supply and significantly reduced the NH4+ supply for 14d in the Brown soil. Differences between the two soils were consistent with results in other studies and attributed to pH and organic matter content differences. The total heterotrophic and Nitrosomonas microbial populations were enumerated using spread plates and most probable number assays. It was concluded that Agrotain® had little effect on the microbial population, where as nitrapyrin reduced Nitrosomonas populations and increased total heterotrophic counts in both soils. Similarity between the results in this study and the literature suggest that the soils in Western Canada have similar responses to inhibitors as those characterized by the literature. Therefore, whether improved nitrogen use efficiency from the use of inhibitors in wheat in Western Canada would be large enough to justify the used of inhibitors will depend on whether local soil properties are conducive to promote volatilization, leaching and denitrification losses of N.
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