Manure is a valuable resource, and you can gain significant value by investing in testing your manure nutrient value, making it more cost-efficient to provide your crops with the nutrients they need.
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Nitrogen fertilizer prices have jumped again, up more than 25% from early this year. Urea and UAN prices have been averaging around 94 cents per pound of N during the first weeks of May. Prices are below the all-time highs from 2022 and 2023, but current and expected corn prices are much lower than at that time. Most farmers likely have strategies for dealing with high nitrogen prices, with manure from dairy and beef production in Wisconsin partially insulating farmers from fertilizer cost pressure (Mitchell 2021). This year, when crop margins are poor, it is important to account for manure as a nitrogen source. In this blog post, we take a quick look at the economics of manure testing to show how accurate nutrient crediting through manure testing can pay for itself and potentially reduce nitrogen spending.
It pays to test your manure nutrient value
Published book values for the nitrogen in manure vary by livestock species, the percentage of dry matter, and when the manure is incorporated (e.g., see Table 9.3 on page 77 of the 2012 version of A-2809), as well as the livestock diet and how the manure is stored and managed. Even if book values account for all these differences, the actual amount of nitrogen in manure varies greatly around these book values. For example, Rayne and Larson summarized the nitrogen content for all manure samples tested by the UW Soil & Forage Analysis Lab from 2015 to 2021. Their Table 1 reports the median N content (roughly the same as the average) and the standard deviation as a measure of variability. For liquid dairy manure, the median was 13.3 lbs N/1,000 gal, with a standard deviation of 6.8 lbs N/1,000 gal. Statistically, these numbers mean that roughly two-thirds of the time, the actual measured nitrogen content ranged from 6.5 to 20.1 lbs N/1,000 gals (13.3 ± 6.8), and one third of the time it was outside these bounds—either higher or lower. This variability is why it pays to test your manure for its actual nitrogen content, so you know how much you actually apply.
Recover the cost of testing manure in just a few acres
Your fertility plan should consider that all the nitrogen in manure is not available for crop uptake in the application year, especially if your manure has lots of dry matter. Also, many farms supplement manure with commercial fertilizer to correctly balance nutrients to match crop needs. Thus, from an economic perspective, what matters is whether the manure test improves your use of commercial N. A manure test currently costs $33 per sample at the UW Soil & Forage Analysis Lab and gives the dry matter, nitrogen, phosphorus, potassium, and sulfur content of the manure. Focusing just on nitrogen, if the test information improves a farm’s N application rate by just 1 pound per acre either up or down, at the current N price of $0.94/lb, the farm would recover the cost of the test over 35 acres (33/0.94 = 35). Given the wide range in the N content of manure, the improvement is likely to be more than just 1 lb N/ac and so be recovered over even fewer acres. Including the value of the P, K and S information means the test cost will be recovered over even fewer acres.
For an extra $8 per sample, the UW Soil & Forage Analysis Lab manure test will also report the ammonium content as N, which is especially valuable for liquid manure. Much like the total N, the ammonium content of manure also varies a lot. Rayne and Larson in their Table 1 report a median of 8.5 lbs N/1,000 gal for ammonium in liquid dairy manure, with a standard deviation of 3.9 lbs of N/1,000 gal for all samples tested by the UW Soil & Forage Analysis Lab from 2015 to 2021. These numbers mean that roughly two-thirds of the samples ranged between 4.6 to 12.4 lbs N/1,000 gal for ammonium content (8.5 ± 3.9). Ammonium is important because it is readily available for crop uptake, as long as the manure is injected or incorporated within a few hours, and so it can substitute for commercial N applications in the year applied.
If the ammonium test information improves a farm’s N application rate by just 1 pound per acre either up or down, at the current N price of $0.94/lb, the farm would recover the cost of the test over 8.5 acres (8/0.94 = 8.5). Again, the wide range in the ammonium content of manure implies that the likely improvement will be more than just 1 lb N/ac and so be recovered over even fewer acres.
The UW Soil & Forage Analysis Lab page for manure testing includes submission forms and instructions for sampling, as well as sample handling and storage. The bottom line is that manure is a valuable resource and much value can be gained by spending only $33 + $8 = $41 to test your manure so you can be more cost-efficient in getting your crops the nutrients they need.
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