By Fabian Fernandez
With high fertilizer prices, farmers are looking for alternatives to make every pound of nitrogen (N) fertilizer count. To be as efficient as possible with nitrogen, the most important thing to do is to rely on best management practices (BMPs) that have been proven through years of unbiased research.
While the discussion is often centered around nitrogen rate, it is important to recognize that nitrogen BMPs encompass much more than just rate. Applying the correct rate of nitrogen while being careless with which nitrogen source you use, fertilizer placement, or timing can lower your nitrogen use efficiency, and therefore your profitability, especially when fertilizer prices are high. In fact, the entire database that we use to calculate the maximum return to nitrogen (MRTN) rate was generated with research trials that use several N rates applied using BMPs. For example, there are no data points from fall nitrogen application.
Having an anchor is a good idea on a stormy lake
Farmers are currently navigating some turbulent waters. It is difficult to predict what fertilizer prices and corn prices will be like tomorrow, let alone this fall and next spring. In these uncertain times, more than ever, it is prudent to stick to what you know for sure: the practices that are backed up by lots of rigorous research and on-farm experience.
If you have attended one of my talks on nitrogen management in the past, you have probably heard me say, “nitrogen management is risk management.” Going with what has shown consistently positive results is extremely important if we want to have a reasonable assurance of success. I have been doing research on nitrogen for a long time now and there are many things that I am not super confident about because the responses I have seen are too variable. However, there are a few things I am very confident about because I have seen them work consistently enough that I feel pretty certain about the outcome. Let me share them with you.
Anhydrous ammonia or urea?
If you are thinking about applying nitrogen in the fall, the only nitrogen source I would suggest is anhydrous ammonia. Looking at 30 site-years of data comparing fall applications of urea and anhydrous ammonia, we found that, 60% of the time, fall urea reduced yield on average by 49 bushels per acre compared to anhydrous ammonia. Using a nitrification inhibitor with anhydrous ammonia adds some cost, but it is worthwhile as it adds an additional level of protection that often is needed to avoid nitrogen loss in the spring.
What tools are out there to improve the efficiency of fall urea?
Some salespeople will try to convince you that urea in the fall is a viable alternative if you are “smart about it.” From many studies where we applied urea after temperatures were below 50F, what I know is that applying urea in the fall with a nitrification inhibitor, using polymer-coated urea, or banding urea (instead of broadcast and incorporated by tillage) did not improve performance of urea in the fall, or the frequency in which we saw a benefit was so low that I would never trust it. So, don’t think you can use any of these alternatives as a “smart way” to apply urea in the fall. It doesn’t work and you will lose your expensive fertilizer investment.
Wait until spring to apply urea
We have 32 site-years of data comparing urea applications done in the fall versus the spring throughout Minnesota in both continuous corn and corn-soybean cropping systems. These studies showed that the economic optimum N rate was 29 pounds higher with fall urea compared to spring application, and yields at the economic optimum were 9 bushels per acre lower with fall urea. Clearly, applying urea in the fall is a lose-lose endeavor. Also, keep in mind that this study finished in 2020, when fertilizer prices were lower relative to the price of corn. Now that you need to produce more yield to break even due to the higher fertilizer prices, the reduction in yield at the economic optimum N rate for the fall application would likely be greater than what we calculated a couple of years ago.
Is this applicable in all of Minnesota?
All of the studies I mentioned above were done in fine-textured soils. We did not conduct this research in sandy soils or in southeast Minnesota because we already know the answer for those parts of the state: you will lose a substantial portion of fall-applied nitrogen 100% of the time. (In addition, fall nitrogen applications are now restricted in certain parts of these regions under the state’s Groundwater Protection Act.)
While what I mentioned in this article is true across Minnesota in general terms, in the south-central part of the state, the potential for a large reduction in yield due to fall urea application is certain. As I mentioned before, when we manage nitrogen, we need to understand what the risks are. In south-central Minnesota, you can be sure that if you apply N in the fall, you will lose a large portion of your investment.
While that’s never a good idea, it is even worse when you are paying top dollar for that fertilizer. You will be better off spending that money on a vacation and actually getting something out of it than buying urea fertilizer for the fall and having to buy more in the spring when your corn turns light green.
Source : umn.edu