Manure applicator injecting into a soybean field. National Pork Board

Dealing with uncertainty in manure

Attempt to remove as many unknowns as possible so that you can get the most value out of the manure applied to your farm’s cropland.

A lot of uncertainties exist in the swine world, and using manure as a fertilizer raises five main sources of uncertainty.

• Nitrogen need of the crop (due to every growing season being different)
• Nutrient content of the manure
• Availability of the manure nutrients to the crop
• Nitrogen volatilization during application
• Application variability and rate uncertainty

Daniel Andersen, Iowa State University assistant professor in the Agricultural and Biosystems Engineering Department, addresses how to deal with these uncertainties in his most recent blog The Manure Scoop.

Andersen suggests minimizing each of the sources of uncertainty, “in some cases this may be practical, in others it might be impossible,” he writes. “For example, manure sampling gives us a good indication of the nutrient content of the manure, but as we all know manure isn’t always consistent, so it isn’t a perfect indicator. One way we often hear people handling this is by adding a little extra nitrogen, some insurance nitrogen, but is that really the best approach?”

Some calculations to find out how this uncertainty impact manure decision making led Andersen down a trail called the “value of information.” Essentially asking if you can now make a better decision because of something you learned from it, how much extra value that adds. “So I did that for manure sampling and was pretty happy, but then someone said, even if I sample I may be more confident about what’s in the manure, but there is still some error in that so maybe I should still be putting on a little insurance nitrogen.”

Andersen used the Maximum Return to Nitrogen calculator to estimate profit per acre after field activities and subtracting the value of the nitrogen applied to the crop above the MRTN rate (because that was nitrogen you could have used elsewhere). “What I found is that uncertainty in how much nitrogen always lowered our profit as compared to if we had perfect knowledge. Probably because there was always a chance of putting on too much nitrogen or too little nitrogen, where if we really knew the perfect amount we could hit the nail on the head.” He found it interesting that when uncertainty does exist, the ideal nitrogen rate was just a little lower than when producers had perfect knowledge.

A few observations Andersen experienced were the chance the manure might have higher nitrogen content “worked to our advantage at low application rates, because there was potential that in the area where corn yield was really sensitive to nitrogen application rate that we actually put a bit more on than we were trying to. However, once we got toward that maximum profit zone we didn’t peak quite as high.” He surmised that was because the uncertainty meant producers were never quite hitting that nail on the head as they might be a little short or wasting a little.

Iowa State University

Figure 1: How does uncertainty change how we should think about nitrogen application? Comparison between perfect and uncertain nitrogen concentration in manure in a corn-soybean rotation (Andersen says 23% uncertain is what using the industry average for your manure is)

 

Iowa State University

Figure 2: How does uncertainty change how we should think about nitrogen application? Comparison between perfect and uncertain nitrogen concentration in manure in a continuous corn rotation.

 

The takeaway from this is that the more we know, the more accurate we can be in hitting the nail on the head and maximizing our profit — “but you already knew that. I mean we say hindsight is 20/20 for a reason, so no surprise there,” he writes.

He found an interesting part was looking at how putting on that insurance nitrogen (just a little extra) impacted the maximum profit. “Essentially what I saw was that a little extra just doesn’t help us handle that uncertainty. Extra N actually hurts us as we are at a spot on the yield response curve that is relatively flat and the risk of wasting extra nitrogen hurts our profit more than the risk supplying that extra N.”

Log on to read this and other “Manure Scoop” blogs by Andersen, aka Dr. Manure.

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