How Do Fertilizer Enhancers Work?
The crop production market has bunch of enhancers - materials to be added to or mixed with fertilizer. Some are legitimate, some not. A typical claim is that they enhance some fertilizer property, often to "improve nutrient availability." That particular claim can be somewhat misleading. These products don't magically react with the fertilizer causing the nitrogen or phosphorus molecules to increase and bud like yeast cells or bacteria. There is still the same quantity of fertilizer nutrient after addition as there was before addition. That is unless so much product is used that the additive actually dilutes the fertilizer.
Legitimate products can be an important nutrient management tool, if used properly. A typical mode of action of a legitimate enhancer is to temporarily block or delay a step in the nutrient cycle. The objective is to prevent or minimize nutrient loss by holding the nutrient in a desirable form until conditions for nutrient loss have passed. For example, nitrapyrin (e.g., N-Serve) delays conversion of ammonium to nitrate for about three to four weeks, reducing potential leaching losses. NBPT (e.g., Agrotain) blocks hydrolysis of the urea molecule to ammonia for about five to ten days, extending the window for soil incorporation of the urea by tillage or precipitation. Fertilizer coatings (e.g., ESN) isolate the fertilizer prill from contact with the soil, delaying any chemical or microbial interactions. In all cases, the activity and the beneficial effect of the additive drops off as time progresses.
Probably the best way to think of enhancers is as a time management tool, extending the window of opportunity for fertilizer application. They are most beneficial when conditions for nutrient loss exist. If conditions are good, then they are essentially an expense. Insurance perhaps, but expense no less.
Fertilizer rate and soil test level are also important considerations. For example, copolymer enhancers are promoted for use with both nitrogen and phosphorus fertilizers with an implication that they work every time they are used. A close look at the research generally shows that - in the limited situations when they do work - both the soil test and the fertilizer rate are often very low. There is rarely a response if the soil test or the fertilizer rate is medium to high. The decision then becomes whether to spend money on the additive or buy a little more fertilizer, either of which may provide the same yield response. It is important to remember that if a product works 5% of the time, it has to return enough profit to offset the costs incurred during the 19 other times it did not work. Fertilizer additives do have a place, but they are most effective when nutrient loss potential is high, when fertilizer rates are low, and when soil test levels are low. If these conditions aren't met, then there is little or no potential return from using fertilizer enhancers.
Fred Vocasek is the Senior Laboratory Agronomist for Servi-Tech Laboratories. He can be reached at 1-800-557-7509 or firstname.lastname@example.org.