Bust the Anhydrous Ammonia Myth

Experts say it doesn't destroy the soil as some claim.

Published on: Jan 27, 2011

Anhydrous ammonia is still the cheapest game in town when it comes to N fertilizer for corn per dollar of N. And there are nevertheless still legitimate reasons not to use it, such as safety, or if injecting on hillsides will open up fields for soil erosion during heavy rain events. However, experts contend that not choosing it just because you think it's bad for your soil is not a valid excuse, or reason for making a decision. They insist it's just not true.

If you've been to any farm meeting at all, especially conservation tillage or no-till meetings, you've heard at least once if not multiple times that anhydrous ammonia hurts the soil. In effect, those who make that statement often say it destroys all soil bacteria, and kills off the earthworm population.

Both Jim Camberato, Purdue University Extension soil fertility specialist, and Danny Greene of Greene Consulting, Franklin, say the evidence simply doesn't support any such conclusion. Instead, Greene's conclusion is that under the current economic conditions, anhydrous ammonia should be a strong contender for the system of choice in most situations.

What does happen, both notes, is that anhydrous ammonia typically wipes out fungi and bacteria in a zone about 3 inches in diameter at the tip of the injection point. Compared to the overall mass of soil in the field, it's a tiny amount. As far as earthworms, if the knife slices one in two, yes, it will kill one.

Soil beyond the zone that forms around the injection point at the end of the knife is not affected, Greene says. You also get a zone of bacteria and fungi kill around the point of injection if you inject 28% N under the soil, such as in no-till situation, but that zone is more like an inch in diameter, which means it's considerably smaller.

Here's the kicker, however. From an N loss standpoint, a bigger zone of kill is actually an advantage. Why? Camberato says it's because the anhydrous kills the denitrification bacteria along with everything else. Bacteria and fungi soon repopulate the soil that was affected. If the zone was bigger, it takes them longer to repopulate it. So bacteria would be back at work denitrifiyng 28% injections before they could repopulate and begin causing losses of N on anhydrous injections,

There's one other point, too, he adds. When you apply 28% N, it's already one-fourth in the nitrate form, easily a target for losses. Anhydrous ammonia is not in that form. The conversion must happen first.