How To Address Fertility Concerns from 2019 Flooding

John Wilson, extension educator in Burt County, Nebraska, and Certified Crop Adviser, shared his experiences in recovering from the 2011 flooding in Nebraska to assist those who are bringing flooded ground from this year back into production in 2020. 

“We had more ground under water than any other in the state,” he says regarding Burt County in 2011. 

In the webinar, Farming After The Flood, Wilson provided details from a 2012 study he helped conduct that included corn and soybeans to learn in an agronomic perspective what role the flooding from the previous year played in the following crop year.

Knowing previous soil test data is key to understanding how flooding may have changed your field’s conditions. 

“Overall, we were surprised that the flooding hadn't caused more of a change to our fertility and that the baseline fertility levels were still there. The grower compared the 2012 soil test results to his past soil tests, and there wasn’t a significant change,” Wilson says.  

Additionally, he said the test site was flooded—without experiencing severe erosion or sediment deposits, which likely would have had different results. 

He shares seven takeaways from the study:

1. Some sulfur levels were high–across the entire area
   Wilson reports he had a number of growers tell him they also saw higher sulfur levels after the flood.
2. The nitrogen levels were normal in the soil tests
   The crew received soil tests showing relatively normal N levels in the soil both in the top 8” and then 8”  to 16.” Wilson says they anticipated low nitrogen levels from leaching and/or denitrification.  
3. Other nutrient levels were also in the normal ranges
   One note, organic matter after the flooding was probably about a half a percent lower than it was before the flooding. 
4. Water infiltration was reduced–this was what we observed not measured 
   The test plots were located on Hayne silt loam and Modale silt loam, which are medium soils with good infiltration. 
5. Corn responded to nitrogen but not to phosphorus. 
   Wilson explains, these soils have 9 ppm in the top soil and 4 ppm in the second 8”. The rates applied via broadcast and banded did not match expectations
6. The corn responded to the cover crops but the soybeans didn't (at least the soybeans, which had to be replanted due to hail damage didn't)
   The site had heavy winds with blowing sand and sediment, which the cover crops did a good job of trapping—up to 4” deep. In some areas, the corn planted after cover crops yielded up to 30 bu. better than areas without a cover crop. 
7. The soybeans didn't respond to inoculate, which we think was due to the residual nitrogen in the soil. 

Here’s a timeline of the 2012 study, which should fill in some of the details of his above observations: 
•    March 26 to 27: Fertilizer applied
•    March 27: Cover crops planted
•    May 9: Corn planted
•    May 10 to 11: Soybeans planted
•    May 12: Glyphosate burndown application
•    May 23: Hailstorm
•    June 4: Soybeans replanted
•    July 2: Glyphosate postemergence

One important note, he said the hail storm on May 23 really threw a curveball, but he thinks the observations they saw are of value. 

Wilson says this study was done with the support of Lee Valley Farms, the Howard Buffett Foundation, Syngenta and Monsanto.  

The webinar is available on playback from the American Society of Agronomy

That is a bulldozer filling in the eroded areas where 7 earth movers and/or box scrapers were dumping sediment (for about 1 month) from other parts of the field. About half the length of the eroded area has already been filled in the above image.

The red X in the image is where the image with the ISU Extension staff was taken (in the image at the top of this article). The red O is about where the pickup in the image below was sitting when it was taken.