Renewable Farming

Next spring, how much of that fall-applied nitrogen will still be in your soil?

Darrell Smith, Farm Journal’s Conservation and Machinery Editor, published on AgWeb Dec. 9 an analysis of fall-applied anhydrous ammonia which is worth close study. It focuses on one more reason we’ve avoided anhydrous on our own farm over the years. 

Dec.10, 2016  By Jerry Carlson The article focuses on the Spring 2016 runoff nitrate pollution risk in Illinois. Weather conditions during fall 2015 anhydrous application were a bit unusual: surprisingly warm soil temperatures and dry soil in much of Illinois in fall 2015, which allowed a surge of stable ammonium nitrogen to convert into the soluble nitrate form — in spite of N stabilizers. That created a high-risk potential for dangerous and costly nitrate pollution of streams in the Spring of 2016.

The detailed report by Darrell Smith says: “In early spring 2016, all the factors were in place for a perfect storm: Nitrification inhibitors often were ineffective because of dry soil. Warm weather caused nitrifying bacteria to convert stable ammonium fertilizer and organic nitrogen in the soil into nitrate. Then late rainfall had moved nitrate deeper in the soil profile. All that was needed for it to enter tile lines and water supplies was rain in April, May and June.”

Fortunately, spring 2016 in Illinois was not as wet as the western Corn Belt, where deluge after deluge flushed out nitrate nitrogen into tile lines and rivers. 

Darrell’s analysis reveals some of the uncertainties about fall-applied anhydrous and the various forms of stabilizers. A key point: The inhibitors don’t work effectively without adequate fall soil moisture. 

Our point in suggesting your review of that article: Back in the late 1960s when I was managing editor of Farm Journal, “Fall Fertilizing” gained favor as a way of spreading out the fieldwork load. Runoff wasn’t much of a concern.

When researchers began measuring nitrogen losses from fall application, inhibitors like nitrapyrin (N-Serve is a widely used brand) looked like an answer in the 1970s. The nitrapyrin inhibits the urease enzyme in Nitrosomas, a nitrifying bacteria. However, it’s a bactericide. In the 1970s there wasn’t much concern about the range of soil organisms that inhibitors might impact. Nor was there much concern about the eventual flushing out of residual nitrapyrin in streams. Today, with intense interest in “soil health” and microbial life, plus nitrate in groundwater, heavy rates of N application are getting closer attention.

The National Laboratory for Agriculture and the Environment has extensive studies on fertilizer runoff. Director Jerry Hatfield organized several field studies upstream of Des Moines, IA to show farmers how to manage runoff from anhydrous and other fertilizers. They were able to dramatically reduce nitrate escape with combinations of filter strips and application changes in selected study areas. But Hatfield told us, “As soon as our financial incentives to participating farmers ran out in the test watersheds, most of the farmers went back to doing pretty much what they had done before. And nitrate runoff rates resumed.”

It’s well-known that knifing in anhydrous kills soil life in the application zone. A few growers like Prairie Hybrids Seed converted anhydrous to aqua ammonia before application, taming down the toxicity. Wendell Owens of International Ag Labs built a water injection system on his anhydrous applicator, which he called a “thunder jug,” for the same purpose. 

But… what happens to the bactericide itself after it’s applied to soil? EPA has long considered it safe, and that it attaches to soil.

Finally this season, U.S. Geological Survey researchers reported results of an initial study of what happens to nitrapyrin bactericide applied to soil. Scientists measuring Iowa streams found the nitrapyrin bactericide in 39% of the runoff water samples taken from March to June 2016. Although the detected levels in streams were well below concentrations which kill animals or soil organisms, the study documents that the inhibitor chemicals don’t degrade readily and totally — as long presumed.

The USGS will continue its study, and broaden understanding of how nitrogen and inhibiting bactericides impact soil organisms. 

Our experience has long favored more microbe-friendly forms of nitrogen, rather than injected anhydrous ammonia. Heavy rates of applied N also make natural nitrogen-building microbes “lazy.” We’ve favored in-furrow, 2×2 row support, side-dress and foliar-fed nitrogen. Those application methods can be tuned with variable GPS rates and timed accurately when the crop needs nitrogen most. 

Naturally, we encourage use of WakeUP to amplify the benefits of spoon-fed nitrogen. Our earliest experience with foliar nitrogen plus WakeUP dates to 2009 and 2010, when field trials showed a substantial increase in yield response when WakeUP was tank-mixed with foliar-fed nitrogen. This chart shows our first field trial.

You can also download a one-page PDF report explaining more details on how the field experiment was conducted. It’s at this link.