Nitrogen stabilizers, what works??
February 26, 2013
Good morning! Since last weeks entry I’ve had a few questions in regards to nitrogen stabilizers and extenders. I recently attended the Nutrient, Soil, and Water Mangement Conference and had the oppurtunity to listen to Dr. Dave Franzen from NDSU give his results on this very subject. He made it very clear that there are certain products that work, and some that have no properties that would be considered a nitrification or urease inhibitor. This morning I will just give you a quick list of what works. Any nitrogen supplied as a commercial fertilizer is ultimately transformed to a nitrate form of nitrogen (or at least a significant fraction of that supplied). In the presence of adequate oxygen, warm temperatures (> 50 F), and some moisture, ammonium-N is converted to nitrate-N through a biochemical process (known as nitrification) that requires two forms of soil bacteria. The first bacterium Nitrosomonas converts ammonium-N to nitrite-N. The second bacterium Nitrobacter converts nitrite-N to nitrate-N. And as you know, nitrate-N is the form we are most concerned about being lost (whether by leaching or denitrification). The first product that works as a nitrification inhibitor is nitrapyrin which is sold under a couple different brand names. Nitrapyrin has been commercially used since the 60’s. There are a couple of different formulations of this product that make it compatible with both anhydrous ammonia, as well as other liquid and dry forms of N fertilizers. Nitrapyrin works by suppressing the growth of Nitrosomonas thus keeping the the fertilizer in a more stable form of N, decreasing the chances of both leaching and denitrification. The next nitrification inhibitor is diyandiamide or more commonly referred to as DCD. This product works in the same fashion as nitrapyrin but is required in higher concentrations. This product is also commercially available in a few different brand names as well. Finally for nitrification inhibitors a person can look at ammonium thiosulfate, or ATS. This fertilizers has shown both nitrification inhibiting and urease inhibiting properties, but is not a recommended product as a replacement because it degrades in the soil much quicker then the other products.
Next we will look at urease inhibitors. Urea based nitrogen fertilizers are an organic commercial form that requires a biological enzyme to promote degradation to ammonia. Ammonia loss potential by volatilization for incorporated urea products is negligible because soil holds enough water to capture ammonia as ammonium that can be held on the soil’s cation exchange complex. Surface applications of urea are at risk of loss because there is no opportunity to capture the ammonia as it is produced. The most common urease inhibitor is NBPT which like the above products is available in a couple different brand names. The NBPT works by locking onto the urease enzyme binding sites, preventing the enzyme from reacting to the urease thereby protecting free urea by allowing it to stay in solution longer, or the inhibitor can inactivate the enzyme.
Application timing, N source, application method, soil texture, and tillage are all factors that should be evaluated to determine where urease and nitrification inhibitors should be used. Before buying an inhibitor make sure scientific evidence backs up its claim. A producer and/or consultant should be wary of any product that does not have solid scientific data demonstrating that the inhibitor activity matches the advertised benefit. If you would like more information please go to www.ag.ndsu.edu/pubs/plantsci/soilfert/sf1581.pdf and check out the information put together by Dr. Franzen. Coming up: The “3rd Wonder of the Corn World”!