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Reducing nitrogen loss from subsurface drainage

September 13, 2022  By Drainage Contractor

A recent Iowa Learning Farms webinar, titled “Influence of fertilizer timing on nitrate loss and crop yield,” presented by researcher Emily Waring

Waring’s primary research focused on managing nitrogen loss from subsurface drainage using in-field practices such as 4R Nutrient Stewardship. The discussed a six-year field study investigating nitrate loss from row-crop fields under different fertilizer application timing conditions. It compares losses between a no-nitrogen control, fall anhydrous ammonia with an inhibitor, spring anhydrous ammonia application and split-applied urea. She also discussed other variables, such as weather, which can add to the complication of nutrient losses to drainage water.

Drainage tile was installed at the field in August 2013, and oats were subsequently planted. In 2014, soybeans were planted to all plots. In 2015, the treatment began.

Waring opened the webinar with a brief review of the Iowa Nutrient Reduction Strategy, a statewide, science-based framework to reduce nutrients to both Iowa waters and the Gulf of Mexico. After outlining the field work and the different fertilizer applications, she discussed the seasonal timing of drainage. She highlighted that in terms of inches, most drainage comes in the spring (April to June), which is both because of precipitation but also because crops use little to no water during that time.


However, what Waring called the “worst-case scenario” occurred between 2015 and 2016. Fall 2015 was irregularly wet – four inches of drainage, which is higher than almost any other season studied – and spring 2016 was even wetter than a typical spring. “In terms of drainage water quality, that’s a very interesting combination, and we’re lucky that we get to see that extreme scenario and how fertilizer timing influences drainage in that extreme scenario where you have no crop growing.”

The webinar is available for free, and offers insight on which fertilizer approaches can best mitigate nitrate losses through subsurface drainage.


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