Managing for soil health is
like managing for rumen health
Elin
Westover, Montana State University Extension, Fallon/Carter County Agent
Many
ranchers are farmers, and many farmers are ranchers. Producers often consider themselves to have
expertise in one area, but generally not both.
However, similarities in the biological systems of each field mean
similar approaches can be used to maximize production in soils and
livestock. Soil functions as a plant’s
stomach, similar to the role of the rumen in ruminant animals (cattle and
sheep). Both the soil and the rumen are populated with microorganisms:
bacteria, fungi, and protozoa. The
function of microorganisms in both systems is dependent on the quality of the environment
and availability of nutrients. Health
and productivity of rangeland and crops as well as cattle and sheep can be attained
by feeding and managing microorganisms and their environment.
1. Microorganisms eat first. To maintain healthy ruminant animals, rumen microorganisms
must eat first, which in turn will feed the animal. When
feed enters the rumen (the second and largest compartment of a ruminant’s
stomach) microorganisms get access to the food source first and break it down
into useable nutrients. For example, rumen
microorganisms break down carbohydrates for their use and volatile fatty acids are
an end product. In turn, volatile fatty
acids are used as an energy source for the host animal. Similarly, the microorganisms in the soil must
break down certain materials before plants can utilize them. Organic forms of nutrients such as nitrogen,
phosphorus, and sulfur are present in the soil either as crop residues or
manure (organic matter) and must undergo a mineralization process before the
nutrients become plant-available.
2. Do not mess with the “bugs.” The
contents of the rumen are partitioned into three layers based on their density.
The upper region of the rumen contains
the gas by-product of microbial fermentation. Grain and fluid-soaked roughage
descend to the bottom region, and newly-arrived roughage lies in the middle. There
are specific microorganisms associated with each layer due to the degradation process
of the specific material. Rumen
contractions are continually mixing the contents slowly. If rumen contents were
vigorously stirred into one homogenous mixture the animal would not perform
normally. The microorganisms’
environment would be completely disturbed and it would take time for their
environment to be re-established and for the rumen to return to normal. The
same idea can be applied to soil, which can be thought of as the plant’s
stomach. Management
tools such as tillage, fertilizer and pesticide applications, and livestock can
be used to improve soil productivity or can be detrimental to soil health if
not practiced correctly. When management
tools are applied incorrectly and do not complement the soil biology, microorganisms
must spend time and energy to re-establish equilibrium with the new environment. For example in the short term, tillage helps
microorganism break down organic matter, but in the long term this loss of
organic matter will hurt soil health and crop yield.
3. Microorganism populations require
time to adapt. In the
rumen, time
is needed for microbial populations to develop and function at beneficial
levels. Furthermore, each microorganism
has a unique function, and depending on the livestock’s diet, the populations
of microbes may need to shift. Therefore
animals must be slowly acclimated to diet changes. It takes roughly 7 days for
microorganisms in the rumen to adapt to a new feedstuff. Livestock producers are encouraged to change
rations gradually, by introducing a new roughage or concentrate source to
livestock incrementally. This allows the
bacteria, fungi and protozoa to adapt and shift ensuring the animal remains
healthy and receives the maximum amount of nutrients from a feed source. Likewise, changes in soil quality and health
will not improve overnight; time is required for microorganism populations to
build to a beneficial level.
4. Carbon: nitrogen ratio is
critical. Health of the soil, like the
health of ruminant animals, will be improved when carbon and nitrogen are in
balance. Microorganisms break down the
protein a ruminant animal consumes and uses the nutrients to their advantage
first. The host animal will then receive
the nutrients in the form of amino acids or nitrogen, or the protein may
by-pass rumen microbial degradation and will be available for digestion in the small
intestine. The “bugs” use the nitrogen
and carbon from protein to grow and their waste provides a portion of the
essential amino acids the animal needs. If
there is a shortage of carbon, the nitrogen cannot be utilized and is excreted
by the animal. If there is a deficiency
of nitrogen, the microorganism activity is reduced and the animal’s growth and
productivity will suffer. Similarly, the
nitrogen waste from the microorganism’s digestion of organic matter in the soil
is what benefits plants. Digested
organic matter can be very beneficial to soil because it helps hold onto mobile
nutrients as well as moisture. The carbon: nitrogen ratio is critical in
balancing the breakdown of organic matter in a slow release fashion. If the ratio is too high, organic matter is
degraded too slowly and the nutrients do not cycle quickly enough between the
soil, plants and microbes. Most plant organic matter has a higher carbon:
nitrogen ratio which inhibits its breakdown. Too much undigested (or composted)
organic matter can rob available nitrogen from live plants as the microorganisms
that break down organic matter need relatively large amounts of nitrogen to
break down cellulose – the main structural component of plants. If the carbon: nitrogen ratio is too low, the
nutrients cycle too rapidly and nothing is left to supply the plant with
nutrients, or oxygen in the soil can be depleted which is necessary for both
microbes and crops. Additionally, when
degradation of organic matter is occurring too quickly, the soil becomes
vulnerable to wind and water erosion, and there is increased evaporation.
5. Dead or alive. Just as microbial activity is important, dead “bugs”
have an essential role in the biological system too. As
the microorganism population in the rumen dies, they are passed to the lower
gastrointestinal tract where they are degraded and utilized as a protein source
by the host animal. Microorganisms
themselves are a great protein source for ruminant animals. Bacteria, fungi and protozoa generally contain
20 to 60 % crude protein on a dry matter basis with bacteria providing the most
at 50% (±5%) crude protein. Similarly, the
microorganisms that die in the soil can also be broken down to supply nitrogen
and other nutrients plants can utilize. This
nutrient cycling is an important facet of soil health and plant nutrition.
6. More is not better. If
you feed cattle more protein than needed, the protein is used as an expensive
energy source rather than a nitrogen source. Additionally, there is a point that it starts
to cost the animal energy to get rid of the excess nitrogen and can cause infertility
due to high pH levels in the uterus. If
you add more nitrogen fertilizer to your soil than is needed, it will not be
efficiently utilized and often lost through leaching beyond the reach of plant
roots or lost as a gas to the atmosphere.
7. Create the ideal environment. Moisture and temperature affect microbial activity while
pH affects the food availability for the microorganisms. Consequently, it is critical to understand
and manage the environment of the rumen and the soil. The rumen
is an effective fermentation vat as long as the environment is anaerobic
(without oxygen) with a constant temperature, pH and moisture content. It is important to note the environment can
change as a result of diet (grain versus roughage diet), but as long as it is changed
over a period of time, the microorganisms can adapt. Diet changes consequently alter the proportion
of volatile fatty acids produced. Like
the rumen, soil can be thought of as a semi-aquatic environment. “Bugs” in the soil are most active in moist,
warm conditions. Each species of
microorganism functions best at a specific temperature and pH. Keeping the soil covered at all times with a
crop or crop residue is one method to help regulate temperature and avoid
extremes. Applications of lime, acid-forming
fertilizers, and other soil amendments can shift soil pH. A soil pH of 7 or “neutral” allows for the
best exchange of soil nutrients and plant roots – too acid and nutrients leach
into the groundwater or streams and too alkaline and nutrients are tightly
chemically bound and are unavailable to
plants. It is always a good idea to test your soil before spending lots
of money to amend it or potentially harm it.
Furthermore increasing the
diversity of the organisms in the soil will provide balance and stability to
soil pH in the rhizosphere, the area immediately surrounding plant roots where
soil organisms are concentrated.
8. Papillae/ villi = Root Hairs. Much
like a shag carpet, the rumen wall is lined with finger-like projections called
papillae. Likewise, the inner surface of
the small intestine is covered with finger-like projections called villi. The size and amount of villi and papillae
change as the diet changes. The function
of papillae and villi is to increase the surface area and therefore increase
absorption of nutrients and water. Similarly, root hairs are very important to
plants and help absorb water and minerals from the soil. Root hairs are small lateral extensions of a
mature root and are visible with the naked eye. Root hairs serve as the primary nutrient and
water uptake mechanism for plants.
Plants’ association with mycorrhizal fungi can also increase the volume
of soil that can be accessed by plants.
Fungal hyphae are like a second set of roots that explore the soil for
water and nutrients. The water and
nutrients that the fungi capture from the soil are provided to the host plant
in exchange for sugars the plant produces through photosynthesis.
9. Diversity.
All microorganisms have a specific role and
utilize specific organic matter. The
diversity of microorganisms in the rumen allows the animals to get nutrients
from the feed consumed. Additionally,
ruminant animals perform better when on a diverse, non-monoculture diet that
provides the microorganisms and animal with a complete diet of nutrients, including
vitamins and minerals. A diverse crop rotation
which utilizes all four crop types (cool-season grasses and broadleaf plants
and warm-season grasses and broadleaf plants) can be very beneficial. One of the benefits of crop rotations and
diversified planting is array of root structures to scavenge nutrients and
water from different levels in the soil and make them available. Increasing plant diversity increases soil
health and soil function by providing the soil food web with nutrient, energy
and water cycling.
10. Continual
and Consistent. Cattle and sheep need access to a
continual and consistent food supply in order to perform to their genetic
potential. Furthermore, the rumen
microorganisms are unable to function to their potential when their feed source
is inconsistent. Likewise, when there
are live plants in the soil, the biology has its preferred food. Organic matter in the soil provides soil
microorganisms with a feed source to break down for the plant. Plants do not thrive in soils that are low in
organic matter because microorganisms have limited access to feed. Both rumen microorganisms and soil
microorganisms suffer from intermittent feed availability.
