By TIM ALEXANDER
BLOOMINGTON, Ill. — Results of the first N WATCH soil testing program, part of Illinois’ Keep it in the Crop (KIC) nutrient management initiative, are available for viewing, the Illinois Fertilizer & Chemical Assoc. (IFCA) has announced.
The nitrogen survey followed the drought of 2012 and was initiated to chart the results of the prolonged dry, hot and humid summer on farm chemical effectiveness and retention.
“We felt it vital to gather scientific evidence of nitrate levels and to track the fate of nitrates through the spring season,” said Jean Payne, president of the IFCA, in an email to members.
“Critics of fall-applied nitrogen normally blame this practice for all nitrate losses, so the N WATCH soil testing program was key to allow the industry to track the fall 2012 applied ammonium in the soil, versus the residual nitrate left for the drought to compare the conversion rates and movement of N.”
N WATCH was launched by KIC in the fall of 2012 by encouraging ag retailers throughout the state to collect soil samples in order to evaluate residual, post-drought soil nitrates.
More than 150 statewide samplings revealed fairly high amounts of soil N last fall, with an average of 19.5 parts per million (ppm) of nitrate-N in the top foot of soil, according to Emerson Nafziger. He reviewed the samplings for the KIC program and published his findings on the University of Illinois’ “bulletin” website.
“Soils represented by these samples had an average of 78 pounds of nitrate-N per acre,” reported Nafziger, a professor of crop sciences for the U of I. “The second foot of soil depth had more than 15 ppm of nitrate-N, which meant another 62 pounds of nitrate-N per acre, for a total of 140 pounds N per acre.”
The fall samplings were conducted, in part, to inventory N in order to determine the potential for loss of leftover soil N. Spring samplings showed only “small departures from normal” in nitrate movement in most areas of Illinois over the six-month period prior to April 1, Nafziger found.
“While nitrate-N moves readily down into the soil profile as water moves down through the soil, the lack of rainfall during the 2012 growing season meant that nitrate from fertilizer N and from soil organic matter simply accumulated,” he said. “Water only moves as far down as it takes to wet the soil, and in a very dry soil, it can take six to 10 inches or more of water to wet the soil.
“Even more water is needed to move through to deeper layers and into tile lines. Indications are that most tile lines in Illinois have been running for the past few weeks in the areas that were dry longer, and for the past couple of months, in areas that received more rain and rain starting earlier.
“Not surprisingly, a few reports in recent weeks from sampling tile line outflow showed elevated levels of nitrate-N. This is normal for spring outflow, but with little or no tile line outflow as N accumulated last summer and fall, and with the large amounts of nitrate we found in fall sampling, the flush of nitrate-N may be larger than normal this spring,” he said.
Do the spring samplings mean anhydrous ammonia applied in the fall of 2012 is still present? Nafziger said while he can’t directly measure how much ammonia from last fall is present, he believes loss of that applied in the fall of 2012 has been relatively small.
Probe samples from corn-after-corn crop fields taken in the spring, while not completely reliable, “found” about two-thirds of the N applied last fall, with about half remaining in the ammonium form.
“Compared to some fall-to-spring changes in ammonium-N reported, we think that nitrification (conversion of ammonium to nitrate) and loss of fall-applied N have been less than normal this winter,” Nafziger reported.
That translates to more residual fertilizers in the agricultural soils of Illinois. The result is not exactly what members of the Illinois Nutrient Research & Education Council (NREC) – which supports KIC and the N WATCH – had hoped to receive after their first year of voluntary soil testing.
“(The report) is extremely interesting reading and very educational not just to our industry, but to anyone who wants to try to understand the complexity of the nutrient cycle and how weather impacts even the best efforts at nutrient stewardship,” said Payne.
The data were extremely important to collect, to ensure policymakers understand how nitrogen reacts to environmental conditions, and to prepare the fertilizer and chemical industry to respond to questions about nitrate movement and nitrate losses as a result of the drought, according to the NREC.
To view Nafziger’s report on the first N WATCH survey results, visit www.bulletin .ipm.illinois.edu/?p=160