Capturing the Most Basic Nutrient: Sunlight

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 nourishment.

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 older leaves.

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 pastures.

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 problems.

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

Balancing Animal Rations for Nutrient Management

For once, it might be possible to please everyone. Good animal production and environmental protection can both be achieved with ration balancing for nutrient management.

When an animal of any species takes in nitrogen (N) and phosphorus (P), only a portion of the nutrients is used within the animal's body for growth and maintenance. Some N and P go into milk, wool, or other products.

Much N and P ends up in manure. Sometimes crop fields can become overloaded with N and P when large amounts of manure are applied to land.

Fortunately, you can control the amount of N and P that animals excrete by balancing their rations. And in many cases, rations that precisely meet animal requirements for production will also minimize N and P excretion. In other words, it is not necessary to trade production for the sake of reducing N and P in the environment!

There are two major strategies for reducing N and P excretion: To help animals use N and P in feed more efficiently, and to reduce the amount of N and P fed.

The first step in these strategies is to set reasonable production goals. If animals are fed for higher production levels than they can reach, extra nutrients will simply be excreted. This is expensive as well as environmentally hazardous. Grouping animals according to their production levels will allow more precise matching of rations to production potential.

The next step is to know the animals and to know the feeds. Nutritionists at the university or feed dealers will be able to supply much more in-depth information about feeds and animals than this article can.

Phosphorus. Animals are able to extract only part of the P from the feeds and supplements they eat. The amount they extract is "biologically available." Of course, the amount they do not extract is "unavailable" - and will be excreted without being used.

Providing feedstuffs which are high in available P helps animals make more efficient use of P in the feeds. So, less total P can be fed than if animals are given feedstuffs low in available P.

Test feedstuffs, including forages, for their nutrient content and find out which feed sources will provide readily-available nutrients to your animals. You may be able to cut back on some supplements - which will reduce nutrient excretion and also expense.

Nitrogen. Avoid excessive protein feeding; it is expensive and causes high N excretion. Setting reasonable production goals and knowing animal protein requirements at different production levels is critical in feeding appropriate protein levels.

Know animal requirements for different amino acids. Feeding high-quality protein supplements which are well-balanced in amino acids will lower the total amount of protein required in a diet, particularly for swine. The use of poorly-balanced protein supplements can cause overfeeding of several amino acids in an attempt to meet animal requirements for one or two amino acids.

For ruminants, particularly dairy cows, consider protein "fractions" in feeds - some feeds contain protein which bacteria break down in the rumen. Cows also need protein which bacteria cannot degrade. If cows do not have sufficient non-degradable protein, they need more total protein.

To reduce total crude protein in the diet and improve milk production, supplement highly degradable protein sources with ones that are not so degradable.

Ration balancing for nutrient management requires a great deal of thought. But keeping high production and profits while maintaining a clean environment is well worth the trouble!

Cromwell, G.L. 1995. Nutrient Management from Feed to Field. Presented at the World Pork Expo, Des Moines, Iowa, June 9-10, 1995.

Grant, R.J. 1996. Feeding Dairy Cows to Reduce N, P, and K Excretion into the Environment. Presented at Area Dairy Days, Nebraska, March 4-8, 1996.
by Victoria Mundy, Extension Educator
Nebraska Sustainable Agriculture Society:

Virgin Prairie: A Disappearing But Important Resource

Virgin prairie was plentiful in the US until the mid-1930s. At that time it was plowed up to plant wheat, as many farmers thought that the prairie had died in the extended drought. In fact the prairie was dormant and waiting for the next rain.

Today many grain producing states contain less than 5% grassland. Only about 1% of that is Virgin native. Much of Nebraska’s Virgin native prairie is located in Pawnee, Johnson, and Gage counties. These are currently the areas of some of the best grassfed beef production in the world. Virgin Native prairie is important as an eco system as well as a basis for production of high quality, nutrient dense beef. It, in effect, is the eco system chosen by nature as the optimal long term balance.

As an eco system, prairie supports several species of unique and rare birds, snakes, and plants. The masasaga rattle snake is almost exclusively found in Pawnee County, Nebraska. The pre-historic looking prairie chicken is also a good example of important species supported by prairie. Bison, whitetail deer, cougars, bob cats, and prairie dogs are found in a variety of tallgrass and shortgrass prairie.

Most important of all is the grass itself. More than 150 species of plants can be found on a healthy virgin native prairie. These each have unique blends of micro- nutrients brought up from the soil and made available to animals and people by the wide range of root depths and soil layers. The grasses and forbs hold the soil from rain and build the soil for further generations.

Contribution by Chris Rohrbaugh