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Benefits of Rotational Grazing by Elli Riemer

May 29, 2018

Soil Health Benefits of Rotational Grazing

It is estimated that America loses 3 billion tons of nutrient rich topsoil every year.  More and more people are starting to believe that the main culprit of this monstrous loss, is the conventionally cropped, tilled and seasonally barren soil surface.  This soil, and the chemicals and manure sprayed on it, is believed by many in the scientific community to be one of the main causes for the Gulf of Mexico and Chesapeake Bay dead zones.  Our soil is being rapidly depleted, and it will require immediate action to restore it. As Franklin Delano Roosevelt said “The nation that destroys its soil, destroys itself.”

        In nature you will never find anything functioning in isolation.  Where  trees exist, there will be birds, vines, shrubs and vibrant soil, all living in symbiotic relationships.  This is one important reason why monocropping is so unnatural, and destructive to soil life.  You never see it in nature.  To have a stable ecosystem, and therefore stable soil, you need biological diversity.

A Glimpse Beneath Our Feet

  Many people believe that soil fertility is governed by chemistry and physics, mainly by the cat ion exchange which allows the soil to hold essential nutrients loosely enough for water to take them up.  Thus conventional soil tests only measure the water soluble nutrients.  This isn’t wrong, there’s just much more going on.  At any given time, only a fraction of the nutrients are in a soluble form.  Conventional soil tests don’t count any of the non-soluble nutrients, and as a result they miss the potential for soil life to work its wonders.

This is where organic matter comes in.  Organic matter is the dead plant or animal material that is capable of, or in the process of, decaying.  Organic matter is one of the main food sources for mycorrhizal fungi.  Mycorrhizal fungi have been partnering with plants in a symbiotic relationship since the beginning of time, with the help of organic matter.  Here’s how it works.   Plants will shed their dead roots and leaves and eventually die.  All this organic matter provides food for the mycorrhizae and in turn, the micro organisms will break down nutrients, modifying them and re-releasing them in other easy to utilize forms.  The plants will then exude a variety of carbon rich molecules which they produce.

Once a critical mass of rhizosphere dwellers is reached they switch gears in what is called quorum sensing.  While they are in quorum sensing, the fungi release compounds to aid plant growth, but when there are too few of them, they turn off the tap.   Thus, all parties involved benefit immensely if there are enough microbes.  The following diagram explains the relationship between mycorrhizal fungi and plant roots.

    

Image result for rhizosphere

The Role Cattle Play in Soil Health

Rotationally grazing is good for this process because, when the cattle are concentrated for short periods of time on any given plot of land, they will eat the first bite of plants, fertilize the plants with their feces and urine and trample the rest.  Most of the plants energy exists in the top third of the plant, which (in a well managed grazing system) is all the cattle eat.  This allows the plants to focus on growing their roots instead of having to replace their stem.  The benefits of the feces and urine include giving an extra boost of nitrogen and phosphorus to the plant.  The trampling requires a little more explanation.  When the cattle trample on the pasture, they help the plant shed its dead leaves, and they can tear the plant.   Whenever a plant is torn, it sends out signals to its micro biome and it will grow back with more vigor.  Also, when trampled, a seed head can get mashed into the ground, planting it.  The impact of cattle’s hooves can push more organic matter and manure directly into the ground and make room for more water infiltration.   This system maintains healthy, natural ecosystems above and below ground.

Plants, when fertilized, on the other hand, do quite the opposite.  They get their needed nutrients from the fertilizers and they stop feeding their microbes.  The microbes then die or move, taking with them the real fertility, and leaving the area bereft of soil life.  Too much chemical fertilizer can also make soils acidic.

Glomalin: Mother Nature’s Super Glue

Mycorrhizal fungi produce a very fine, long and branching structure called hyphae.  Hyphae are one of the main modes of growth for most fungus, and they can penetrate very hard surfaces in the soil.  They also expand the area from which a plant draws water and nutrients, by funneling them to the tips of the plant roots.  After the microbes produce hyphae, they exude glomalin.  Glomalin is a protein that is much like a polymer coating, and it seals up the holes in the hyphae.  This helps the hyphae to transport things more efficiently.  Glomalin also aggregates the soil by binding the particles together, and sealing holes, which allows further water infiltration.  Glomalin is a carbon-based substance and mycorrhizal fungi are carbon-based molecules.  Therefore both depend on carbon, and that is why it is so important that glomalin keeps carbon stable in its sticky substance.  Rotationally grazing is good for microbes, which is good for glomalin, but conventional tilling injures and tears it.

Rotationally grazed pasture is great for water holding. The cattle trampling creates more mulch and organic matter, which reduces runoff, creates drought resilience, and promotes greater soil moisture.  Land can -in the proper rotations of cattle and cover crops- hold 16 inches per hour of water. 

When plants breathe in carbon and breathe out oxygen, the carbon they take in does not feed themselves but their biomass.  When plants are grazed, they send out distress signals in the form of carbon rich molecules, and their microbes then kick it into high gear.  In 2006, the United Nations Food and Agriculture Organization (FAO) released a report called Livestock’s Long Shadow, and in the report, they blamed meat for 18% of all greenhouse gas emissions.  However, very little of this applies to grass-fed beef.  For one thing, most carbon dioxide used for raising beef comes from big tractors and equipment used produce feed grain and cultivate the fields the grain is grown on.  Second, that 18% counts deforestation, which is used to make more grain fields, and which has no relation to grass-fed beef.

The FAO said in a 2013 report “Grassland soil carbon sequestration could significantly offset emissions.” In a Soils Association report, they said that “Grass-fed livestock has a critical role to play in minimizing carbon emissions…”  Manure, rotations, cover crops and composing are all beneficial to carbon sequestration and soil life in general.   When you till up prarie or pasture you release all of that stored carbon into the air.

Ongoing scientific research shows that rotationally grazing is much better for the soil and, in turn, it gives you much more grass and less weeds than continuous grazing.  At the Virginia Middleburg Experiment Station, in the 1950s, they did a study on continual grazing versus rotational grazing.  They had started with two of the same size fields and the same pasture planting.  The field representing rotationally grazed pasture was divided into six paddocks and the cattle were moved once a week. The other field was continuously grazed.  The experiment went on for five years, and after five years, in the continually grazed pasture the weeds doubled, and the legumes halved.  After five years in the rotationally grazed pasture, weeds halved and legumes doubled.

  Cattle can reverse desertification.  Desertification is the process where overgrazing or ongoing crops will cause  

  a desert to be formed.  When managed properly, the disturbance of concentrated hooved animals breaks through hard desert crust and allows plants to grow.  Cattle also fertilize the ground, increase organic matter and increase water infiltration and water holding, which is very important in the desert!  The pictures above are of the same plot of land before and after a few years of intensive rotational grazing. Grass needs either grazing or mowing to help it shed its dead leaves, and cattle do a great job with it.

Some people include other animals in their rotations, and this diversification can be even better than cattle alone.   The benefit of doing that is different animals eat different plants, or parts of plants, and they dung and urinate different nutritious things.

If cattle can do so many amazing things, why are they vilified?  Well, cattle can do amazing things when put in the right system, but in the wrong system they can wreak havoc.  If you don’t rotate them, you will destroy the land and the grasses will become fewer and fewer and weeds will multiply.  Many people have this idea that fewer cattle means less impact, but that is not true.  You can cause overgrazing by having to few cattle.  The natural way for cattle to move is in huge herds and to keep moving away from predators and from the soiled grass.  Under this system, there were lush pastures across the great plains, where now there is nothing but depleted topsoil from conventional farming.

Cattle can work miracles in the dessert and rejuvenate old dead pastures and crop fields.  Cattle can store away carbon in the soil and help slow down climate change.  These animals are great at feeding the microbes and the other soil life, and in turn create bountiful pastures.   They increase organic matter and water infiltration.  So, is rotationally grazed pasture better for the soil than conventional crops?  No question about it.

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