Keywords: Nitrification, Nitrification inhibition, DMPP, Nitrate losses.

Nitrification inhibitors delay the nitrification of applied nitrogen in soils by temporarily suppressing the oxidation of ammonium nitrogen. They are an effective means of reducing environmental problems related to nitrate in agricultural soils and in increasing the efficiency of fertiliser nitrogen. Although several chemicals are known to reduce the rate of nitrification, only a few comply with the requirements for commercial products. The active ingredient has to depress the oxidation of ammonium to nitrite to avoid a build-up of nitrite in the soil, it must not be phytotoxic, toxic/ecotoxic and must behave acceptably in the environment.

By preserving applied ammonium nitrogen, leaching of nitrate as well as emissions of gaseous compounds like nitric oxide, nitrogen dioxide and nitrous oxide during nitrification and denitrification are reduced. Its effective period must last long enough to bridge critical periods of under-developed root systems or reduced nitrogen need of crops, but it must phase out to provide enough nitrogen when the growth of the crops accelerates.

Only two products had been introduced successfully into the market (2-chloro-6-(trichloromethyl)pyridine in North America and dicyandiamide in Europe). BASF Aktiengesellschaft has in recent years started the development of the new substance 3,4 dimethlypyrazole-phosphate (DMPP) which is highly effective and can be fixed within granular fertilisers. The high effectiveness of DMPP also renders its use economic in general agriculture. The product gives no cause for concern with regards to toxicology, ecotoxicology and behaviour in the environment. It was shown that nitrate leaching was reduced – depending on the water regime of the soil – by about half, and that the emission of greenhouse gases decreased by a comparable amount.

Farmers and vegetable growers benefit from its use by either reduced nitrogen rates or increased yield, by a lower number of fertiliser applications and – often – improved quality and increased proportion of marketable yield. Leaf vegetables show a darker green and thus look more attractive, several vegetables species have a lower nitrate content at harvest and the starch content of potatoes is often improved. While a lower protein content is preferred for malting barley it might be a disadvantage for milling wheat; it is therefore recommended that a conventional nitrogen fertiliser is used for the top dressing of this crop.

The new nitrification inhibitor DMPP from BASF achieved registration in several European countries and has been well accepted in its first commercial season.

Drs Wolfram Zerulla, Karl-Friedrich Kummer, Alexander Wissemeier and Matthias Rädle, Fertilizer Development, BASF Limburgerhof, Germany.

23 pages, 12 figures, 3 tables, 37 refs.