Nutrient Reduction is More Than Cover Crops

When someone mentions nutrient reduction, one of the first things that comes to mind is planting cover crops.  Cover crops are a good solution, but not the only one.  A recent study points out that farmers must take the next step beyond cover crops if we are to effectively reduce nutrients.

That study is “Increased extreme precipitation challenges nitrogen load management to the Gulf of Mexico” was published in Communications Earth and Environment in September 18, 2020, by Chaoqun Lu, Jien Zhang, Hanqin Tian, William G. Crumpton, Mathew J. Helmers, Wei-Jun Cai, Charles S. Hopkinson, and Steven E. Lohrenz.

The researchers stated “Our study suggest that special attention should be paid to the effectiveness of N reduction practices during hydroclimate extreme events, extreme precipitation in particular.”  They noted, “On average, the reduction in N yield during non-extreme precipitation days accounted for two-thirds of the annual total reduction, leaving one-third to the extreme precipitation days”.  Further they state, “up to 16% of annual N load could be potentially reduced during 1980-2017 by removing fall application and applying N fertilizer after planting, without harming the productivity of major crops.”  The study defines extreme precipitation as “days with daily precipitation over the 90^th percentiles in each month.”

As that study stated, “Basin-wide, extreme precipitation events occurred only 8.6 days a year (2.4% of 365 days) on average, but they contributed to approximately one-third of annual total water yields and N yields.”

In other words, those 8.6 days account for one-third of the nitrogen contributed to the Gulf of Mexico.  With this study in mind, it makes sense to apply fertilizers to fields after they are planted and, therefore, the crops are more likely to utilize the fertilizer.  Second, it makes sense to increase the number farms implementing techniques that retain storm water and then filter it, such as edge-of field practices (bioreactors and saturated buffers), stream buffers, wetlands, grassed waterways, increased soil carbon, no-till farming. 

Sources

Chaoqun Lu, Jien Zhang, Hanqin Tian, William G. Crumpton, Mathew J. Helmers, Wei-Jun Cai, Charles S. Hopkinson, and Steven E. Lohrenz, “Increased extreme precipitation challenges nitrogen load management to the Gulf of Mexico”, Communications Earth and Environment, September 18, 2020

“ISU finds nitrogen runoff tightly linked to extreme rain”, Corridor Business Journal, September 21, 2020