URBANA, Ill. — Midwestern soils are among the most productive in the world, thanks in part to extensive tile drainage systems that remove excess water from crop fields. But water isn’t the only thing flowing through tile drains. Nitrogen moves along with soil water into drainage ditches, streams, and ultimately into the Mississippi River Basin, where the nutrient contributes to massive algal blooms and hypoxic conditions that impact aquatic life in the Gulf of Mexico. 

A recent study from the University of Illinois Urbana-Champaign provides a new look at the sources and processes affecting the nitrogen load in tile drainage water. The study reveals an unexpectedly large and stable “legacy” pool of nitrogen, adding nuance to the common belief that nitrogen pulses rapidly through tile drainage systems as a transient reflection of fertilizer input and microbial activity.

“The legacy effect relates to the time lag between when nitrogen is made available in the soil environment to its loss to waterways. For example, if you have a nitrogen input via fertilizer this year, it won't be reflected in offloads downstream immediately. This lag has been found in many systems, but previous researchers didn't know what caused it or how large its magnitude was,”  said lead study author Zhongjie Yu, assistant professor in the Department of Natural Resources and Environmental Sciences (NRES), part of the College of Agricultural, Consumer and Environmental Sciences (ACES) at Illinois.

Read the full release from the College of ACES.