Nitrogen rate management (MRTN) is the low-hanging fruit of the Iowa Nutrient Reduction Strategy, a win-win for profitability and the environment. On closer inspection, that fruit is even juicier than we thought; but harder to reach.
Here’s the paradox of nutrient management that the general public fails to grasp. We don’t know with any certainty at application time how much nitrogen the corn crop will need or how much nitrogen will be left in the soil come July when the crop starts maturing. Corn stalk nitrogen tests and split applications can improve the accuracy of the guess, but farmers still have to guess. If they guess too low, they lose income. So most farmers err on the high side, which means that (all else being equal) more nitrogen will end up in our streams.
Figure by John Sawyer at ISU. The economically optimum nitrogen rate varies by year, even on the same field.
We may not know what’s the right amount of nitrogen to apply this year, but we can pinpoint a range that makes the most economic sense across sites and years. In 2005, Iowa State University researchers crunched the numbers and developed an online calculator. A farmer can enter current prices for corn and fertilizer to get the Maximum Return To Nitrogen (MRTN). Above that range, they might get a bit higher yield, but the revenue from those extra bushels doesn’t offset the cost of the extra nitrogen. Applying nitrogen at the MRTN is a rare win-win for profitability and the environment.
Along with cover crops, wetlands, and bioreactors, MRTN was one of the more promising practices for nitrogen outlined in the Iowa Nutrient Reduction Strategy. Still, the authors cautioned that it wouldn’t get us very far by itself. An average field would cut nitrate losses by 10 percent. Since some parts of the state apply less nitrogen than others, universal adoption of this practice would get us a 9 percent reduction in nitrate concentrations.
That modest reduction assumes Iowa farmers currently apply 150 lbs of N/acre on a corn-bean rotation and 190 lbs/acre on continuous corn, a figure the authors admitted were “possibly outdated.” A 2017 survey by ag retailers found that Iowa farmers apply 169 lbs/acre of nitrogen on corn after beans and apply 210 lbs N/acre on continuous corn. I updated Dr. Helmers graph with those numbers and an MRTN based on current corn and nitrogen prices to determine the potential water quality benefit. This low-hanging fruit is juicier than we thought!
And that’s just the average! Inspired by a recent essay by Chris Jones, I read a manure management plan for a field in one of our watersheds. It receives 190 lbs/acre of nitrogen and 146 lbs/acre of phosphorus in the form of liquid swine manure. If that manure could be spread over more acres at a rate of 140 lbs/acre, that could reduce nitrate losses by 31%. If it replaces rather than supplements commercial fertilizer, we could get another 4% cut in nitrate. Manure is a slow-release fertilizer and less susceptible to leaching.
Is that economical? Hard to say. Daniel Anderson reports that liquid swine manure can be moved seven miles and still be cheaper than synthetic fertilizer. In Story and Boone County that might work. Hamilton County has 218 manure management plans, so I’m not sure how far you’d need to travel to find a field not already being treated. Are there changes in processing or additional cost share that would help make it more feasible? I don’t know. No-one is talking about it. But cover crops work equally well. Winter rye grows thicker with fall-applied manure and can scavenge nitrogen that would otherwise be lost.
Unfortunately, neither of those options (MRTN or cover crops) are even suggested as part of manure management plans and the loudest voices in the room are saying livestock producers don’t need to be doing anything differently. Until that situation changes, the widespread adoption of rate management that’s assumed in statewide and watershed-based scenarios won’t happen and we will fail to meet our nutrient reduction goals.
Several of our staff attended the Iowa Water Conference on March 12 and 13. The event brings together hundreds of smart, hard-working people that are working to improve water quality, restore aquatic habitat, and control flooding across the state of Iowa. We always learn a lot from both the presenters and the other attendees, and come away energized. Here are our top three lessons we learned this year:
1. Farms can simultaneously improve water quality and wildlife habitat
Adam Janke, Extension Wildlife Specialist, talked about how the practices being used for nutrient reduction can also benefit many of Iowa’s species of greatest conservation need. For example, trumpeter swans like CREP wetlands. Migrating ringneck ducks and Topeka shiners use oxbow wetlands. Meadowlarks use prairie strips. We will be pursuing these kinds of synergies in three watersheds with a National Fish and Wildlife Foundation grant, so it was great to hear specifics.
2. Retailers of agricultural products need to be part of water quality solutions
Chris Jones from University of Iowa shared some disturbing data from northwest Iowa. In the Floyd and Rock River watersheds, livestock production and manure application has doubled since 1980, but commercial fertilizer sales have remained the same. In those watersheds, nitrogen is being applied at 80-100 lbs/acre above the MRTN (Maximum Return to Nitrogen), leading to nitrate concentrations in the Floyd and Rock rivers that are twice as high as other streams in western Iowa. Clearly, some farmers aren’t thinking about their manure management plan or water quality when they purchase nitrogen fertilizer, and their retailers aren’t bringing it up. When our conversations about agriculture remain siloed (pardon the pun), water quality suffers.
However, at another session, we learned how ag retailers with the Agriculture’s Clean Water Alliance are showing leadership on water quality — including water quality monitoring in the Raccoon River and developing a code of practice for nitrogen application to reduce losses from farm fields while increasing return on investment (ROI). Precision agriculture tools are also being used to identify land where inputs aren’t generating a good ROI, and use that information to make conservation decisions that benefit both the bottom line and the environment. Gregg Schmitz of Nutrien shared an example where revenues from a 140 acre farm were increased by putting 70 acres into CRP and redeploying inputs into the other half. Surveys show that agriculture retailers and crop consultants are trusted sources of information for farmers, so their involvement will be essential to solving our water quality challenges. We’re grateful for the support of Key Cooperative and Heartland Cooperative on field days and producer engagement in the Squaw Creek watershed.
3. Water quality improvements are possible, but require a commitment of both time and money
Neil Shaffer, an award-winning watershed coordinator in northeast Iowa, shared some heartening success stories. Nitrate leaving the Staff Creek and Beaver Creek watershed was reduced by 47%. Brook trout were reintroduced to a tributary of Silver Creek. In both cases, it took over 8 years of monitoring and $3-5 million of funding for conservation practices to see those changes. We’re well aware that water quality requires a long-term commitment and are in this for the long haul.