Total Pageviews

Sunday, October 1, 2017

Composting barns

I've just read an article on composting barns  in our local farming magazine.  We are re-inventing the wheel but that is OK.  I saw this system in 1989 in South Africa and they had been using it for some time.  So what are they.  First a little background science.

You can classify the break down of organic material into simpler substances which are available for the growth of plants, into two main types.  This break down can occur aerobically or anaerobically.  The results are different.  With anaerobic break down, the processes are less energetic and two significant by-products are ammonia, NH4, and Hydrogen sulphide, H2S, (which in the air oxidizes to Sulphur dioxide and water.  SO2  H20). Both Ammonia and Hydrogen sulfide are gases and go off into the air.  In doing so, they  take with them the valuable nutrients Nitrogen (N2) and Sulfur (S). 

Aerobic processes are far more vigorous since the strong oxidizer Oxygen (O2) is present and only produce Carbon dioxide (CO2) and water.  In aerobic break down a whole ecology of microfauna build the available nutrients into their body mass. Aerobic processes can use cellulose and lignin as a source of Carbon and energy*.  In anaerobic processes, both are refractory. As long as the source of organic carbon lasts, the waste products of each trophic level are built back into body mass by the primary producers*.  Finally in this system, as organic carbon runs out, nutrients are released in a form that plants can use.  The ecology runs down and the final product left is Humus which has some interesting benefits for the soil.

*  In a photosynthesis system, the primary producers are plants.  In the sea, they are primarily single cell algae and sea weed.  In a compost pile they are micro-organisms and if the source of carbon and energy is wood (cellulose) then the micro-organisms which produce cellulase, the enzyme that can cut off the sugar mollecules from the cellulose are the primary producers.

In a composting barn, you provide a source of carbon in the form of saw dust or wood shavings. You could also use pelleted paper or any other source of cellulose.  Cellulose is an interesting substance.  It is a poly-sacaride.  In other words a chain of sugar molecules joined together in an insoluble form.  No multi-celled animal can digest this material.  Some bacteria, on the contrary, produce cellulase*.  While algae are the primary producers in the sea, cellulase producing micro-organisms are the base of the food chain  in a cellulose rich compost.

Enzymes are named for the substance that they can catalyze the use of.  Hence the enzyme that helps metabolize sucrose would be called sucrase while the enzyme that metabolizes cellulose is cellulase.

Of course the cellulose is not enough for these micro-organisms.  They need the other nutrients such as nitrogen, phosphorous, sulfur and so forth to build their bodies.  They scavenge these from the environment and they themselves become food for a whole range of grazers who build these substances into their bodies.

As a rough rule of thumb, each level in the trophic chain can incorporate about a tenth of the material from the level below it.  A ton of phytoplankton can make a tenth of a ton of Krill which can make a hundredth of a ton of whale.  The remaining 90% at each transfer goes back into the soup to be used again by the primary producers.

As long as there is a source of energy, such as sunshine in the case of phytoplankton or cellulose in the case of a compost pile, all these nutrients are re-incorporated into biomass.  When the energy source runs out, there is a net release of nutrients as the various micro-organisms feed on each other but with no energy and Carbon source to power  the uptake of the released nutrients*

* This is why it is so bad to mix saw dust into your soil.  All the free nutrients will be scavenged until the saw dust is used up.  Then nutrients will be released and the plants can start to grow again.

So how about composting barns.  In these barns there are a number of requirements.  First, you need a thick layer of cellulose as bedding.  The urine and dung of the animals living in the barn (or visiting it) is absorbed by the saw dust or wood shavings.  The farm we visited in South Africa used the coarse saw dust from a saw mill.  But that is not sufficient.  The bedding must be kept aerobic.  In Africa, where I first saw this method, they were growing chickens.  This is possibly easier than growing cows because the urine of birds is almost solid.  Cows, by contrast, produce copious amounts of urine.  Labor in South Africa at the time was not expensive and the saw dust bedding of the chickens was stirred each day by hand.

In the case of a cow shed, one would have to have a mechanical method of stirring the bedding.  Cows go for milking and in some systems, go to graze during the day. giving a perfect time to aerate the bedding.

Note that the metabolism of all these wee beasties in the compost give off heat just as you and I do when we metabolize.  The bedding is warm and it has been reported that given a choice, cows will bed down in these barns in preference to staying outside or going into stalls with straw on the floor.

As you can imagine, ventilation is of the greatest importance as well.  No poisonous gases such as Ammonia or Hydrogen sulphide are given off but Carbon dioxide is produced.  A sloping roof with vents at the top of the slope and good access for air from the sides is vital.  The heat from the bedding and the not inconsiderable heat from the cows will create a natural convective circulation.  It is also useful to place the watering troughs outside the shed wall so that the cows can access it but so it does not drip down into the bedding. Moisture is needed for the activity of the compost bed but too much makes it very difficult to maintain aerobic conditions.

 Also useful would be to have drop down curtains, especially on the side where the heavy weather comes from so that rain can be excluded from reaching the bedding.

In really cold climate, one could employ a really large heat exchange ventilation systems which uses a counter flow system to pass outgoing air past incoming air to keep the heat while exchanging the air.  Such systems are used on as smaller scale in air-tight houses today.

When we talked to the farmer in South Africa who was using this system for Chickens, he mentioned as an aside how disease free his chickens were under this system.  Apparently any pathogens that fall into the bedding are on a hiding to nothing.  The environment is inimical to their survival and they are destroyed by the rich fauna of composters.  Another article I read on cow sheds using this system emphasized the same phenomenon.

To recap, what are the benefits of this system.

* Animal welfare.  The very fact that cows vote with their feet and choose to bed down on the compost in preference to staying out in the cold or going to a straw lined stall shows how beneficial such a system is.  It is highly likely that in such a system, the amount of milk per unit feed would increase as the cows are using less energy to keep warm and are less stressed.

* Nutrient retention.  All the nutrients from the waste products of the cows is held in the compost to be later used to enrich the soil of the farm.  Nitrogen and Sulphur do not go off as gases to be lost to the farm.

* Odor control.  The smell of a well aerated compost is faint and pleasant in great contrast to an anaerobic compost.  The neighbors are not annoyed.

* Disease control.  There are strong indications that diseases are reduced with this system.  It is likely, for instance,  (though not yet reported on) that mastitis would be reduced when the cows bed down on a compost bedding.

No comments: