Nitrogen fertilizer and nitrification inhibitor impacts on soil N dynamics

Blucher Menelas, Purdue University

Abstract

Of the nutrients necessary for plant growth, nitrogen (N) is the most limiting nutrient in agricultural soils. Maintaining soil N levels in agricultural fields to ensure crop yield performance is challenging due to the complex dynamics of N transformation in soils. Laboratory studies were conducted in soils varying in organic matter, cation exchange capacity, and texture to further our understanding of band-injected anhydrous NH3 and the influence of nitrapyrin-based nitrification inhibitors, (a N-Serve™ formulation commercially available since 1976) and Instinct. (a recently developed microencapsulated formulation) on nitrification of band-injected urea-ammonium nitrate solutions (UAN). In a separate study we quantified the kinetics of nitrapyrin release from Instinct™. In a laboratory study, the retention of NH3 and the distribution patterns of exchangeable and fixed NH4 +-N and subsequent NO3--N production via nitrification were influenced by available moisture content and its spatial distribution, soil types and properties such as pH, clay and organic matter contents. The trends in NO3--N production across soils and experiments were inversely related to soil clay and organic matter contents. The linear regression slopes across soils and experiments for net cumulative NO3--N were significantly different (P < 0.01) and the NH4+-N pool depletion reflected similar order for both runs of this study: Pinhook > Raub > Chalmers > Pewamo. We observed significantly less NH4+-N disappearance when UAN was treated with Instinct. compared to UAN alone. However, the simulated spring xx temperature regimes clearly demonstrated the impact of soil temperature alone to provide protection of indigenous and applied N as microorganisms responsible for nitrification or denitrification were either inactive due to low temperature or they did not reproduce to a population size capable of rapid conversion of NH4+-N to NO3 --N. When comparing the performance of both formulations of nitrapyrin (Instinct™ and N-Serve™.) with band-injected UAN, we found that the percentage of added NH4+-N nitrified across soils was less in the UAN plus N-Serve™. treatment compared to the UAN plus Instinct™ treatment. Although N-Serve™. was found to be slightly more effective than Instinct™ in this study, further laboratory and field evaluations across a wider spectrum of soils and environmental conditions are needed before strong conclusions relative to the efficiency of this new formulation of nitrapyrin can be made. The kinetics of nitrapyrin release study showed that only 14% of the added nitrapyrin was released from Instinct. microcapsules over a 70 day incubation period in distilled, deionized water. The daily rate of nitrapyrin release ranged from 0.16-0.17%. Dow AgroSciences (patent holder) suggest that microcapsule wall thickness, core:coat ratio, microcapsule size, pH and temperature could all play important roles in the release kinetics of microencapsulated nitrapyrin. Therefore, studies that include these factors are essential for a more thorough understanding of nitrapyrin release from Instinct™ microcapsules.

Degree

Ph.D.

Advisors

Camberato, Purdue University.

Subject Area

Agronomy|Soil sciences|Environmental science

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