Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu
Amendments to prevent the loss of nitrogen (N) were studied in a recent Agronomy Journal article: “Evaluation of Nitrogen-Loss Prevention Amendments in Maize and Wheat in North Carolina” (Vol 109, Issue 5, pp 1811-1824). Of all of the soil nutrients, the N cycle is the most complex, with potential losses coming from leaching or volatilization as a gas.
Products meant to prevent N transformation into easily leached nitrate (NO3) or gasses like ammonia (NH3) have been used for years, with updated formulas and new products coming onto the market. This study observed three products:
1) NBPT-DCD (Agrotain-Plus, Koch Agronomic Services LLC, Witchita, KS),
2) nitrapyrin (e.g. Instinct II, Dow Agrosciences LLC, Indianapolis, IN), and
3) an organic glycol combined with Calcium (organo-Ca).
NBPT-DCD has both urease (converts urea N to ammonium) and nitrification inhibitors. Nitrapyrin only inhibits nitrification, which is the conversion of ammonium to nitrate, a form which is easily leached out of the crop root zone. The final product, organo-Ca, was suggested to act like a surfactant, while manufacturers also claimed that a pH change prevented the conversion of ammonium to the gas ammonia. The authors listed Nzone (AgExplore International, Parma, MO) as an example of an organo-Ca products.
For this study, all three products were mixed with UAN and added to soil types from North Carolina (Coastal Plain, Piedmont and Mountains) and incubated in the lab. Most of Delaware is Coastal Plain, but we do have some piedmont soils in the north-western part of the state. For both the coastal and mountain soils, nitrapyrin performed well at reducing nitrification (ammonium to nitrate), still working 84 days later. NBPT-DCD performed better than the organo-Ca and UAN alone in the coastal and mountain soils, which both reached zero ammonium at 28 and 56 days, respectively. Essentially, adding the organo-Ca was similar to applying UAN by itself.
The piedmont soils observed losses of nitrogen immediately, likely due to the finer texture and moisture content of the soils. In those saturated conditions, nitrate can rapidly convert to nitrogen gas and volatilize from soils. The remaining ammonium was protected by both NBPT-DCD and nitrapyrin.
Besides incubations with soils in the lab, the authors also tested the products in the field. Results from trials on corn and wheat revealed that weather and N-rate (increasing rates of N) were more significant factors in yield than any of the products. The plots treated with all three products did not provide yield advantages, or increased N use efficiency or uptake. High rainfall in wheat, which should leach out any nitrate, showed no observable differences either. So while the incubation studies did reveal that nitrapyrin and NBPT-DCD could prevent conversion to nitrate, it did not correlate to greater yields in the field.