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
|
|
Soybean
(Fragile Residue) |
Corn
(Non-fragile residue) |
||
|
|
%Residue
Coverage |
% of
Residue
Remaining |
%
Residue
Coverage |
% of
Residue
Remaining |
|
Broadcast
|
74
|
96
|
90
|
99
|
|
Disk
incorporate
|
24
|
30
|
57
|
62
|
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