For more than a century, researchers have sought an accurate method to measure nitrogen content and needs of soil. Tests have come and gone, but farmers continue to rely on a mathematical equation based on desired yield with adjustments for manure and other nitrogen sources. That approach often leads to adding fertilizer that a crop simply can’t use, say University of Illinois soil fertility experts.
Enter Richard Mulvaney, a professor of soil fertility in the department of natural resources and environmental sciences. He has developed the first test – using Mason jars – to detect chemical fractions in soil that feeds corn plants. His Illinois N Test sorts the fraction of amino sugars from nitrogen in soil. “We expect to eventually be able to tell a farmer exactly how much nitrogen his soil can use,” he said.
Researchers place a sample of dry soil mixed with a dash of sodium hydroxide into the jar. Hanging from the lid is a petri dish containing a dab of boric acid solution. While sealed, the jar is heated at 120 degrees for five hours. Amino sugar nitrogen in the soil is converted to gaseous ammonia and collects in the petri dish. Using titration, researchers then determine how much nitrogen is in a sample that could potentially be delivered to plants.
Mulvaney described his research in October at the annual meeting of the American Society of Agronomy in Charlotte, N.C. In November, Robert Hoeft, a professor of soil fertility in the UI crop sciences department, demonstrated the test at two regional soil fertility meetings in Iowa. “The response has been fantastic, and there is a sense of urgency,” Hoeft said. “They want it now.”
Just begun is a one-year study in which researchers will take samples weekly from three fields in East Central Illinois to track changes in the amino sugar nitrogen content. “We hope to be able to take a sample in the fall and predict nitrogen availability for the next growing season,” Mulvaney said.
How accurate is the test? “If someone applied manure 17 years ago, this test will detect it,” said Saeed Khan, a research specialist in Mulvaney’s lab. A high concentration of nitrogen in one sample was traced using old site maps to just outside the gate of a pigpen, where manure was often dumped.
If additional experiments prove the test is ready, Khan said, manure could become a valuable recyclable commodity, nitrate runoff could be reduced by better management, and Mason jars – used for storing fruits and vegetables since their patent in 1858 by John Landis Mason – would have a new use.
“At first glance, it looks silly and seems almost amazing that a Mason jar could be used for this purpose,” Mulvaney said. “But the fact is that the Mason jar is the key to this whole test. It is in effect an extraction system and the best one I’ve ever seen.”