Monday, March 30, 2015

Finishing up does better nutrient conservation pay? The incorporation part of the story

The recent post on nutrient conservation was supposed to be an evaluation of why we often inject or incorporate our manure, but I only really got injection covered. So I thought this week I’d try to do a part two, where I focused on incorporation of some solid manures (since we don’t have commercial options for injection of solid manures available quite yet – at least not many, though I have seen one or two homemade systems as well as some research systems).

Example of the USDA-ARS developed by Dr. Pote. Manure is ground up prior to injection to facilitate the actual injection.

So here, I am going to use examples for two types of manure, beef solid manure and poultry layer manure. Based on the ISU publication, using manure nutrients for crop production it looks like we’d expect between 15-30% of our applied nitrogen to be lost to volatilization if we broadcast a solid manure and don’t incorporate it. Alternatively, if we broadcast apply it and leave it on the surface for a while before we incorporate it, such as if we were applying manure in the winter but could not incorporate until spring.

There are a few ways to approach this topic. The first is, were you going to do some tillage anyway? If so, then we would have paid for the tillage operation anyway, so the cost may be close to $0/acre. However, though this may in principle be true there may be a time cost associated with having to conduct the tillage operation at a time close to when the manure was applied. That is, what might need to purchase new or larger application equipment to adjust when we are playing manure or we might need to pay for additional labor to make sure these operations get accomplished at roughly the same time. The other option was that no tillage was going to be performed, so adding that tillage operation represents are real cost. In either case I’m going to treat these cases the same, and use data from the 2015 Iowa Farm Custom Rate Survey, to estimate the cost of incorporation. Based on my look through the document it looks like it would cost somewhere around $15 per acre to get an incorporation operation performed.

Beef feedlot manure

To perform an economic comparison, we need to know what manure application rate we are planning to use. Often times solid manures are applied based on phosphorus management decisions. This often makes about 10 tons per acre a reasonable application rate for beef manures; though it will depend based on your crop rotation, the current soil phosphorus levels in your soil, anticipated crop yields, and the nutrient content of your farm’s manure so considerable variation about this number could exist based on your production system and management objectives.

If you made me guess, I’d expect about 20 lbs N/ton of manure from a feedlot. This means that if we are applying 10 tons per acre we’d be putting on 200 lbs of nitrogen (this may sound like a lot as a typical recommendation for corn following soybean is around 150 lbs/acre), though only about 70 lbs/acre would be available in the first year. This means we were probably thinking about side-dressing some nitrogen to supply our crop with the rest of its nitrogen need. Anyway, our question becomes would hiring someone to get our manure incorporated at the time of application pay for itself in terms of nitrogen savings? In this case we are anticipating losing 15-30% of our applied N if we don’t incorporate quickly, so this would amount to about 30 – 60 lbs of N per acre, or about $13 to $26 worth of nitrogen value being conserved. So in this case it looks like it would justify the $15 per acre cost of incorporation.

Layer manure

In the case of layer manure I’m going to assume an application rate of about 4 tons per acre. In this case I’m estimating the manure has about 37 lbs N/ton (and about 24 lbs N per ton that would be available in the first year). At this application rate, I’d be applying almost 150 lbs N/acre (of which about 100 lbs N/acre would be expected to be available in the first year). In this case if we lost between 15-30% of the applied N to volatilization, we’d be losing 20 to 45 lbs of N per acre, which amounts to about $10-20 an acre worth of value. This again would put us right in the range were incorporation would just about pay for itself, especially if we were doing the tillage anyway and just need to adjust when it is performed.

Other thoughts

So this is just a little wrap-up with a few concluding thoughts. It may seem like I’m promoting incorporation pretty vigorously in this post, and I am, but I certainly understand there are instances when incorporation may not make sense. One good reason for doing this might be erosion. Limiting erosion is often about leaving residue on the surface of the soil to help protect it, any time we perform a tillage pass some of the residue will be lost. I have seen numerous studies that have shown manure application without incorporation may reduce erosion, at least in some situations. Thus, as with most things it is about weighing the benefits and costs and figuring out what best works in your farm. Is nitrogen conservation most important or is it potential erosion and soil loss? In either case are there additional changes you could make to protect against that concern or is this approach the best option.

Percent of initial residue cover remaining after manure application/incorporation

(Fragile Residue)
(Non-fragile residue)

% of Residue
% Residue
% of Residue
Disk incorporate