Get the most bang for your buck: time your manure and anhydrous applications well

October 14, 2021 10:28 AM
Blog Post

With rising fertilizer prices, and concerns about possible shortages, it pays to time our applications of anhydrous ammonia and manure well. When the value is high, the focus on management is even more important.

Anhydrous costs are reported to have risen to $850 or more per ton.

Using typical swine finishing manure nutrient concentrations (50-15-30 pounds N, P2O5, and K2O per one thousand gallons) and fertilizer prices last year, the fertilizer value of manure was around $35 per one thousand gallons. Today, with MAP, Potash, and Ammonia prices that are rising to nearly twice as much as last year, the value of this manure is as high as $65 per one thousand gallons.

As an example, at a common finishing swine manure application rate of 4,500 gallons per acre, that value sums up to $292 per acre. The cost to haul and apply manure will vary but can be around two cents per gallon. In this example, that application will cost you in the ballpark of $90 per acre, still leaving a net value of $202 per acre. That is a lot of potential value that farmers are especially happy to have this year.

But are you getting the most bang for your buck with your manure or anhydrous applications?

Application of liquid manure and anhydrous ammonia should wait until soil temperatures are 50°F and cooling. That usually occurs in early November. Although we recently experienced a cool-down from unseasonably warm temperatures, forecasts aren’t indicating that this 50°F goal will occur any earlier than normal. Warmer soils will drive nitrogen conversion and increase the risk of nitrogen loss. The warm weather has kept soil temperatures high across the state, ranging from 60°F in NW Iowa to over 70°F in SE Iowa on October 10th. Anhydrous and manure applications made in 60-70°F soils are undoubtedly risky and could easily lead to significant losses of nitrogen. For manure, the nitrogen value accounts for upwards of half of that $292 per acre manure fertilizer value.

Keep an eye on your area soil temperatures here.

Is applying anhydrous ammonia or manure when the soil temperature is well above 50°F really a problem? Yes, even with a nitrification inhibitor. Ammonium in the soil does not leach with excess water moving through the soil profile, but nitrate does. Although we seem dry now, that leaching risk, and loss of useable nitrogen, occurs in most springs. The rate that the ammonium from the anhydrous application, or the ammonium in swine manure (about 80% of that total N), moves to the nitrate form of nitrogen does not actually stop until we have soil temperatures at the freezing point. The rate of movement to nitrate at 50°F is about 20% of the maximum rate, still not fully stopped, but greatly reduced. The rate is about 50% of maximum at 60 degrees and jumps to 70% at 65 degrees.

Nitrification, the movement of ammonium to nitrate, is carried out by microbes. Banded anhydrous does kill those microbes and slows the process where it is at a high concentration. However, the recovery of that microbe population and resumption of nitrification occurs faster when the soils are warmer. That would be true for nitrification inhibitors, also. Manure applications do not have the concentrated band of ammonium temporarily slowing the microbial activity.

It makes clear economic sense to delay manure application until the soils are cool in the fall.

Recent ISU research trials (research has since been updated) found a 4-year average of 38 bushel per acre corn yield reduction when manure was applied after soybean harvest early in the fall when soils were still warm, compared to waiting for soils to be 50°F and cooling. With $5 per bushel corn prices and high fertilizer costs, it pays especially well this year to delay your fall application until the soils are cool: potentially in the neighborhood of $190 per acre more in yield and a nitrogen fertilizer cost savings of $142 per acre (again with a 4,500 gallons per acre application rate).

Applying manure in the fall, especially when applied before the soils are cool, creates risk of nitrogen loss. ISU research shows that planting a fall cover crop can reduce nitrogen loss from early fall applied manure, highlighting the importance of using cover crops when application timing is earlier than ideal.

It also makes economic sense to increase the number of gallons applied in the spring, up to a point that is feasible. The same study also found a 28 bushel per acre corn yield benefit to applying in the spring, compared to the late fall application into cool soils. Learn about some new technology for spring manure side-dressing and more on application timing here.

To get the most value out of the phosphorus in the manure, prioritize fields with lower soil test phosphorus for manure application. If you are adding manure to fields with high to excessively high soil test phosphorus, you are not utilizing that manure phosphorus value well (around $64 per acre, in our example).

Lastly, don’t forget about equipment maintenance.

Equipment calibration and maintenance are also critical for getting the most value from your manure nutrients. Research at ISU found that there can be a drastic amount of variation in manure application uniformity across the toolbar due to neglected maintenance issues. Air vents on the manifold can accumulate manure and plug as the manure dries out. Vents should be checked prior to application and cleaned as needed. Eliminating hose loops and fixing crimped hoses will also help improve uniformity across the toolbar. You can check for issues by putting several hundred gallons of water in the tank and starting the pump with the injectors out of the ground. Flow should be relatively uniform across the injection toolbar. Read more about toolbar uniformity here.

Additional resources:

Fall Fertilizer Nitrogen Application:

Application Checkpoint for Fall Anhydrous:

DNR Manure Application Separation Distances: DNR 113 Separation Distances for Land Application of Manure and DNR 117 High Quality Water Resources.

Manure Timing Impact on Yield:

Improving crop yields and water quality with manure management:

How to Sample Manure for Nutrient Analysis:

Manure Monday: Manure Application and Timing: 

Calibrating Liquid Tank Manure Applicators:

Distribution of Liquid Manure Application:


Joel DeJong Field Agronomist in NW Iowa

Joel DeJong has over 20 years of experience working closely with farmers on integrated management of pest populations, crop management issues, and nutrient and manure management planning. As the extension field agronomist in northwest Iowa, he currently educates crop producers on proper nutrient ...