Fertility: Meshing Old & New

cover_dec09For fertilizer efficiency, the new products and the old standbys complement one another.

By Glen Harris

When fertilizer prices reached an all-time record high, the market seemed to be flooded with new products designed to increase fertilizer efficiency. At the same time, there was a movement to get “back to the basics” and go with what we know works. In fact, the fertilizer industry rolled out a campaign to practice the “four Rs,” i.e. using the right source, the right rate, the right place and the right time for fertilizer.

So which is it? New products? Or the old standbys? Well, the answer is both.

The reason the answer is both is because the new “enhanced efficiency” or “EE” fertilizers – that include products such as urease inhibitors, nitrification inhibitors, slow release, controlled release and additives such as humates and acids – can come into play with all four Rs.

For example, when considering the right source, some growers recently shifted away from using ammonium nitrate to using granular urea, mainly due to cost and availability. However, nitrogen (N) from surface-applied urea can be lost into the air by volatilization. That’s where urease inhibitors, which can reduce this N loss, come into play when choosing the right source.

Right Rate, Right Place And Right Time
Choosing the right rate of fertilizer is probably the most important R. Don’t get me wrong, all four Rs are important, but there is probably more money lost by missing the right rate of fertilizer (high or low) than anything else. How do the new EE fertilizers come into play with rate? If using an EE fertilizer truly results in increasing the uptake of fertilizer nutrients by a plant, then a grower can really zero in on the correct rate.

Notice I did not say you can automatically reduce your rate, since it depends on if you were using the correct rate to begin with. Of course, growers are always encouraged to apply the correct fertilizer rates as determined by soil test results and recommendations.

EE fertilizers and the right time or timing of fertilizer applications obviously go together when it comes to slow and controlled release fertilizers. If a slow release product can eliminate a trip across the field, or a controlled release form can deliver nutrients to a growing corn crop exactly when it needs it, then more economical yields can be reached. Nitrification inhibitors, which can improve N use efficiency by slowing the conversion to the nitrate – the leachable form of N – especially in sandy, irrigated soils in the South is another example of how new EE products and timing interact.

How fertilizer placement and the new EE fertilizers interact may not be as obvious as the other three Rs, but they do interact. For example, some new EE products are designed to increase the availability of phosphorous in starter fertilizers. Starter fertilizers are already designed to place the nutrients close to a young growing plant, and the EE fertilizer may enhance this effect.

Nutrient Uptake, Maximum Economic Yields
Even though I have given examples of how EE fertilizers and the four Rs interact separately, it is easy to see how they can come into play all at once. Using our starter fertilizer example again, you pick out the right source of fertilizer and add an EE to it when accounting for the right rate (based on soil testing), the placement (close to the seed) and timing (at planting). All of these together should result in increasing the rate of nutrient uptake and obtaining maximum economic yields. Some of the old and some of the new. Together.

Contact Glen Harris, University of Georgia (UGA) Extension soil scientist at (229) 386-3006 or gharris@uga.edu

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