Does better nutrient conservation pay? The story of injection and incorporation

A common question we ask is how much you should be willing to pay for conservation, but now and then, the stars align, and initiating a conservation practice at your farm makes you money. One example I discussed earlier was the case of manure sampling. Sampling helps you use your manure resources better and saves you money (you can check out this old post here: http://themanurescoop.blogspot.com/2014/10/economic-value-of-manure-sampling-and.html) by helping better manage your manure as a fertilizer resource.

Let’s take the time to talk about another practice – injection. So the approach of this little write-up will be to explore how the costs of manure management change with the surface application instead of injection/incorporation and how the benefit we get from our manure changes.

Swine Manure

Let’s start with swine manure. In working these calculations, I’m going to be working with what I consider to be average swine manure from a finishing operation with a deep pit, something like 60-30-25 (N-P2O5-K2O) pounds per 1000 gallons.

In this case, we are working with liquid manure, and it makes sense to perform injection/immediate incorporation rather than just surface applying. One reason to do this is that it places the phosphorus below the ground surface, which helps protect it from surface runoff and keeps it there when we need it. However, the primary reason for injection/immediate incorporation is nitrogen management. Getting the manure in the ground, mixed with soil, and covered reduces the amount of nitrogen we lose through volatilization.

So let’s work on some examples to see how these practices compare. In the direct injection of the manure, we do an excellent job of limiting ammonia volatilization, reducing it, so it is typically between 0-2% of the total amount of nitrogen we applied. If we had just surface applied this liquid manure, we’d expect that between 10-25% of our nitrogen would be lost. So, what value does this have at our farm?

Alright, so let’s assume we are working in a corn-soybean rotation, and we plan to apply our manure at the maximum return to nitrogen suggested rate. In Iowa, this would mean our ideal rate (based on current corn and nitrogen prices) would be 134 lbs N per acre that we want to supply to our crop.

In the injection system, to do this, we’d need to apply about 2400 gallons per acre because we are getting about 56 lbs of available N per 1000 gallons of manure. I adjusted the total amount of N in the manure times and availability factor and a loss factor to calculate this. I used 95% available in this case, based on ISU PM 1003, which suggests swine manure will be 90-100% available, and correct for nitrogen losses during application by multiplying by 0.99, which assumes 1% of the applied N will be lost to volatilization.

134 lbs N/acre / (0.99 * .95 * 60 lbs N/1000 gallons) = 2400 gallons per acre

If we had surface applied without incorporation how would have this changed? Well, we’d still have the same manure and I’d assume the same N availability, but my correction for ammonia volatilization would be different. In this case, I’d assume that between 10 and 25% of the applied N would be lost. We’d have to apply closer to 2900 gallons per acre.

134 lbs N/acre / (0.75 * .95 * 60 lbs N/1000 gallons) = 3150 gallons per acre

So what does this mean? We’ll I had to apply an extra 750 gallons of manure per acre to get the same crop production, reducing the number of acres we cover with our manure. This means we are applying, and wasting, about $18.50 worth of extra nitrogen value.

The second part of this question is how did my costs change? To estimate this I need to do some quick estimating about how this would affect my manure application expenses. It’s not perfect, and every situation is different, but to get a rough cause of the cost I use the figure below.If we had surface applied without incorporation, how would this have changed? Well, we’d still have the same manure, and I’d assume the same N availability, but my correction for ammonia volatilization would be different. In this case, I’d assume that between 10 and 25% of the applied N would be lost. We’d have to apply closer to 2900 gallons per acre.

134 lbs N/acre / (0.75 * .95 * 60 lbs N/1000 gallons) = 3150 gallons per acre

So what does this mean? We’ll I had to apply an extra 750 gallons of manure per acre to get the actual crop production, reducing the number of acres we cover with our manure. This means we are applying and wasting about $18.50 worth of extra nitrogen value.

The second part of this question is how did my costs change? To calculate this, I need to do some quick estimating about how this would affect my manure application expenses. It’s not perfect, and every situation is different, but to get a rough cause of the cost, I use the figure below.

So, how do you use this graph? The blue diamond graph represents injection while the red squares represent broadcast (we could talk about why the charts have different shapes, but not today). In the injection case, we said we wanted 2400 gallons per acre. Using the top line, I’d estimate an application cost of about $0.02 per gallon, which would give an application cost of approximately $48.50 per acre. In the case of surface application, we wanted 3150 gallons per acre, which has an application cost of around $0.01 per gallon, or about $30 per acre. That means injecting cost us about $18 more an acre, while we only saved an extra $18.50 worth of nitrogen value. In this case, the value of the conserved nitrogen covered our additional application expenses.

Dairy manure

So, what about dairy manure? In this case, I estimate dairy slurry will have about 25 lbs N/1000 gallons, which will be about 35% available.

Using the same assumptions as before, I’d calculate a manure application rate of 15,000 gallons per area to supply 134 lbs N to our corn crop, while for surface application, it would be 20,000 gallons per acre. In this case, I’d estimate an application cost of about $0.011 for injection (total cost of $169 an acre whereas in the case of surface application, the price was about $0.0078 per gallon (total cost of $159 an acre).

The extra 5,000 gallons would contain about $19 worth of fertilizer value, once again making injection a great choice to increase the value of your manure and to help protect the environment.