Capturing the Most
Basic Nutrient: Sunlight
by Wyatt Fraas, Center for Rural Affairs
Most discussions of nutrients for crop or
grazing lands begin and end with the mineral
elements, like nitrogen, phosphorous, and
potassium. Livestock discussions also include
vitamins and amino acids. Water is another
critical nutrient for growth, reproduction and
maintenance. But sunlight is the most basic
nutrient of all. Plants depend on sunlight to
photosynthesize their food. Livestock depend on
plants, or animals that eat plants, for
At the most basic level, farmers and ranchers
turn sunlight energy into products to use or
sell. Plants convert sunlight into food and fiber
for animals and people. Farmers can sell or eat
the plants, or they can harvest them to feed
livestock. Allan Savory of the Center for
Holistic Resource Management describes this
process in the above graphic.
Unfortunately, solar energy is lost at each of
these steps. About 6% of the energy that hits a
plant can be turned into more plant material.
Only about 10% of the plant's energy is available
as food for plant-eaters. The rest is lost to
decay, or is used by the plant. Only about 10% of
the energy in those plant eaters is available to
predators. The rest is lost as heat, or through
body maintenance and decay. Only about 10% of the
energy in the predators is available to humans
and other critters who feed on meat-eating
animals like fish, poultry, and bears. This
energy forfeited at each conversion is truly lost
- neither we nor other living organisms can make
use of it. Fortunately, this energy flow is
constantly replenished by sunlight.
How do we improve our collection of solar
energy? Farmers and ranchers control the time
when plants convert sunlight to plant material. A
mix of 'warm' and 'cool' season grasses in a
pasture, for example, will convert sunlight
throughout the growing season. Young leaves are
slightly more efficient at photosynthesis than
Producers decide how much land area is covered
by sunlight-trapping plants. Crop planting
density directly affects the number of plants in
a field that are converting sunlight energy into
useful forms. Cover crops make use of otherwise
bare ground between rows, during fallow periods,
or before and after crop growing seasons.
Farmers and ranchers also control the volume
of plant leaves that trap sunlight. Leaf area
varies with the type of plant, as well as the
planting density. Tall plants with broad leaves
will intercept more sunlight than short plants
with narrow leaves.
Tallgrass prairie provides a natural example
of how time, area and volume interact to capture
a maximum of sunlight energy. A wide variety of
plants, including grasses, legumes, forbs and
trees, grow from the spring thaw through the hot
dry summer, until the fall freeze. Some of these
plants remain green throughout the winter.
On the native prairie, patches of soil are
sometimes bare of green leaves. Annual plants use
these spaces between perennial plants in the
spring and fall, while a canopy of taller plants'
leaves covers those spots in the summer. Not too
long ago, bison and other grazers periodically
fed on and then avoided parts of the prairie.
Modern management-intensive graziers mimic this
pattern to maintain nutritious, fast-growing
Technology can enhance the land's ability to
capture sunlight. Fertilization can make plants
healthier, bigger, or more numerous. Pest
controls can keep plants healthy, and irrigation
can extend the growing season into dry periods.
But technology costs money, which can only be
recovered through increased plant production.
When wealth is generated from on-farm resources,
it can be measured in "solar dollars."
Plant production supported by outside resources,
such as petroleum energy, is subsidized by
non-renewable "mineral dollars."
Mineral dollars have brought many material gains,
but our dependence on mineral resources has
resulted in air and water pollution, wildlife
losses, and social inequities, among other
Allan Savory proposes that generating wealth
from sunlight is the smartest choice we can make:
"...we can generate income from human
creativity, labor, and constant sources of energy
such as geothermal heat, wind, tides, falling
water, and most of all the sun....
"A characteristic of wealth derived from
this combination is that it tends to not damage
our life support system or to endanger
mankind.... A further characteristic is that it
is the only form of wealth that can actually feed
people." Quotes from Holistic Resource
Management, Allan Savory, 1988, Island Press
Nebraska Sustainable Agriculture Society: Home Features