The science of manure, including its management and handling, options for treatment, use as fertilizer, the impact it can have on the environment, and new technologies being developed to improve its use. In this blog I strive to provide a scientific perspective and really dig into the issues. This blog is brought to you by Iowa State University Extension and Outreach. Follow me on Twitter @DrManure or find me on Facebook at Iowa State Manure and Nutrient Management Lab.
Did you know it is the World Health Organizations Antibiotic
Awareness Week? In light of this, I decided it was a good week to look at antibiotic
resistance bacteria in manures. Now this isn’t a topic I consider myself and
expert on so I’m going to be borrowing heavily from my college at Iowa State, Dr.
Antimicrobials, such as antibiotics, are used in the
livestock industry at therapeutic levels for disease treatment. Once the
antibiotic has been administered, the animal will begin to metabolize it (break
it down), but not all of it is metabolized, some is excreted with the feces and
urine, ending up mixed with the manure. For example, in the case of tylosin about ¾ of
the mass administered to an animal ends up in the manure.
Why does this matter? Well once these compounds are in the manure
they put a selective pressure on the microbes in it to become resistant to that
compound. It is sort of like this, if its cold outside you can stand outside
and shiver or you can put a jacket on. For microbes it’s sort of the same thing;
the presence of that compound might negatively impact most of the microbes, but
perhaps a few of them will figure out to put a jacket on (become resistant to
that antibiotic). Then when the manure is land applied as a fertilizer, these resistant
bacteria enter the environment. If it happens to be a microbe that makes people
sick and they come into contact with it there is a chance that our normal
antibiotics might not be as effective for this guy, because it already has some
built up tolerance to it. Sure, there are lots of ifs in this case – are they
in the manure to start with, how long do they last, does the animal and human
antibiotic even work in the same way (similar mechanisms) – but that’s what
people are trying to find out.
Picture of Enterococcus
So in a recent study Dr. Soupir performed she tested how swine
manure application (fall applied swine manure at 168 kg N/ha, or about 150 lb
N/acre compared to spring injected UAN) and tillage practices (chisel plowing
versus no-till) impacted the persistence and transport of enterococci; both
total enterococci and those resistant to tylosin (a type of bacteriosat that
was used at the farm the manure was obtained from).
So they measured lots of things in this study but what we
are going to focus on is enterococci (and tylosin resistant bacteria) in the manure
(at the time of application), in the soil (both in the fall after manure was
applied and in the spring), and in tile water over the following growing
season. They found that the manure had between 90,000 and 570,000 colony
forming units per gram of manure and that between 70-100% of these bacteria
were resistant to tylosin. When it came to the soil samples, they tested both
in the manure application band, outside the manure application band, and in the
control plots that didn’t receive manure. Not surprisingly, enterococci
concentrations were the greatest in the manure injection band, and lowest in
the control soils that didn’t receive manure. Concentrations of enterococci between
the manure bands were similar to the non-manured soils. Over the winter,
enterococci concentrations decreased by about 70 and by the time the manure had
been in the soil for a year had returned to levels equivalent to soils not receiving
manure. No difference in enterococci concentrations in the tile drainage water
So where does this leave use? At least during this study,
when weather conditions were drier than normal for Iowa, it doesn’t appear that
manure injection changed the risk of to water quality. However, different
weather conditions where it is wetter during and after manure application, may
impact these results.
A publication detailing this study is available at:
Check it out if you are interested in learning more.
I grew up on a small dairy farm in Central Wisconsin – we
milked about 40 cows and had 110 acres where we grew mostly corn and forages.
Our forages were always a mix; alfalfa-grass mixes (seeded with an oat covercrop that was
turned into oatlage that first year) in our “good” fields, clover mixes in our
wetter fields where alfalfa didn’t do as well. In some years maybe even some
sorghum sudangrass (often in a hayfield that winter killed that we had to tear
up or that corn field that didn’t get planted because it was too wet).
So why an I reminiscing about perennial forages? The Iowa nutrient
reduction strategy (Reducing Nutrient Loss: Science Shows What Works - https://store.extension.iastate.edu/Product/Reducing-Nutrient-Loss-Science-Shows-What-Works)
says that adding 2 years of alfalfa to a 4 or 5 year rotation can reduce
nitrogen loss by 42% and it will help reduce soil and phosphorus loss as well. It provides perennial ground cover for periods of the rotation after all. So the
questions that has been on my mind is what would motivate farmers to raise more alfalfa (or actually any
perennial forage)? Has it been replaced by another forage like corn silage? I
ask these questions because at least one way of potentially getting more
alfalfa on the landscape is to encourage more ruminant animal production as
they can use the forage to make human food – meat and milk.
To get us started on this conversation I looked at survey
data from the National Agricultural
Statistics Service. The first thing I pulled was alfalfa acres by year from
1950 through 2015 in both Iowa and Wisconsin. Back in 1950 there was about 4
million acres of alfalfa in each state, now there is a little over 1 million in
Iowa and 1.6 million acres in Wisconsin. When I look at this graph I see some
similarities – both states have seen pretty drastic reduction in alfalfa acres
over the 60 years shown, but one big difference. Iowa started losing alfalfa
acres before Wisconsin did. Iowa alfalfa acres have been on the decline
since about 1955, while Wisconsin stayed pretty steady in alfalfa acres until
about 1990. So why have these acres been on the decline?
To supplement this I also took a look at corn silage acres,
hypothesizing that if we were going to grow less alfalfa perhaps corn silage
was replacing it in rations. It was interesting to me that I didn’t really find
this at all – Wisconsin corn silage acres today are almost the same as they
were back in 1950, and while Iowa’s corn silage acres are also similar to their
1950s levels they are still well below the levels we saw throughout the 60’s,
70’s, and early 80’s. Apparently that wasn’t the missing piece to the puzzle,
but then I looked at total corn silage production (tons raised per year), and
it held a partial answer – for Wisconsin at least. Though corn silage acres haven’t increased, corn silage production had, especially since 1990 (when we started seeing less alfalfa acre). If you plot alfalfa acres in Wisconsin versus corn silage production
you get a petty strong relationship of alfalfa decreasing with more corn silage
- a pretty good indication that corn
silage is replacing alfalfa, maybe not on the landscape but in our dairy
rations. Better corn silage yields are freeing up land that had been used for
alfalfa to grow other crops. So this answers
part of my question – more ruminants won’t necessarily lead to more alfalfa on
the landscape – but also says it could, we just have to understand what drives
the decision of alfalfa versus corn silage a little better (another topic for
another post though).
However, it did not answer my question about alfalfa production
in Iowa; but if we look at cattle on feed and corn silage production in Iowa we can see that they do trend together. As cattle on feed peaked in the early 1970s corn silage production was growing and peaked shortly after was well. Indicating that corn silage and cattle were linked. This doesn’t explain where our alfalfa acres went, but
it does show that more ruminants won’t necessarily
lead to more alfalfa. There are other important factors in deciding between alfalfa
and corn silage.
So where do we go from here? Adding alfalfa (or other perennial forages) to the landscape
can have numerous water quality benefits and could potentially open additional
opportunities for feeding more ruminants. However, based on history it appears the opposite approach,
getting more ruminants on the landscape may not have the same effect. That is
just because we have more ruminants doesn’t guarantee more perennials for
forages. If we are going to strive for more perennials, ruminants can be part
of the answer, but it will also require a conscious decision to choose the perennial
instead of corn silage.