How to establish and keep forage legumes

Walt Davis 2007

Published in The Stockman GrassFarmer

In the early 1970’s we were running Davis Ranch in southeastern Oklahoma as a high tech beef cattle, pecan and crop operation and were following all of the land grant college recommendations as to fertilization, weed and insect control. We routinely used 100-150 pounds of actual nitrogen on our cropland, almost that much on Bermuda grass pasture and were producing a lot of product. Production was high but so was the cost of production and all too often we found ourselves losing money on every pound we produced and trying to make up the difference by producing more pounds. This was the period when conventional wisdom was “get big or get out” and efficiency of scale and specialization were the buzzwords of the “agricultural experts”. In 1974 the cattle market broke, as it had about every nine years for over 100 years, and we found ourselves in serious financial trouble. After ten years of trying to “do it right”, we had the choice of changing the way we operated or going broke. A look through our books made it crystal clear where the money was going; fertilizer, machinery upkeep, chemicals, fuel and labor expenses were all much too high. We had taken a very simple business based on natural biology and changed it into an industrial monster with an insatiable appetite for expensive inputs. One of the largest of these expenses was nitrogen fertilizer. We decided to halt nitrogen use on pasture and instead use forage legumes to supply this need. This started what my wife termed “Your annual sacrifice to the clover gods”. This was not an inaccurate statement, as I knew very little about growing legumes and it would be several years before I learned enough to give the clovers a chance. The extension recommendations of the time still called for applying nitrogen fertilizer to new legume plantings even though research by Dr. Bill Knight and others had shown that as little as sixteen pounds of actual nitrogen could kill all of the rhizobia bacteria on an acre of sandy soil. By trial and error, over a period of years, we learned how to establish and keep a high percentage of legumes in our forage sward at a reasonable cost. We were intensifying our grazing management at the same time that we were introducing legumes and quickly learned that the two practices fit together like a hand in a glove. When we got enough paddocks to control exactly what our stock was eating at any point in time, it became much easier to maintain the legume mix and also to prevent bloat and maximize animal performance. The benefits of legumes in a complex pasture mixture go far beyond merely reducing cost.

Truly successful forage plans rely on the concept of complex forage swards maximizing days of quality graze over time. This is considerably different from the more common concept of judging pasture solely on the number of tons of forage produced per acre per year. The value of a pound of green forage at any point in time is directly proportional to the abundance of forage at that time. The extension literature is full of figures showing exactly what it costs to grow forage and how to reduce the cost of forage by applying nitrogen fertilizer to increase yields. These figures reflect the short-term cost of the forage but do not reflect the value of this forage in a grazing operation. If coastal Bermuda grass is nitrated in May or if fescue is nitrated in March, yields of forage will be greatly increased. In both cases, the increased production comes during the time period of peak production and aggravates an already severe problem of forage distribution over time. To be consistently profitable, grazing operations must maximize the percentage of the total ration that comes from grazing. No mechanical forage harvest system can come close to competing in cost to the grazing animal. In an on going grazing operation, a major goal should be to provide, in a graze able form, both the quantity and the quality of forage needed to supply the needs of the livestock present for as many days of the year as possible. To do this requires having green and growing forage for as much of the year as is feasible. Plants are classified as warm or cool season according to their growth habits but there are also differences by species and within species as to time of growth within a season. Complex mixtures of forage plants consisting of different species of warm and cool grasses as well as forbs and shrubs both legume and non-legume can capture more solar energy and provide more days of quality grazing than is possible with monocultures or with simple mixtures. The complex mixtures are also much more stable in their ability to deliver forage in the year-to-year time frame and are of tremendous value in reducing weed pressure.

Legumes are unique among plants in that they have the ability to form a symbiotic relationship with a class of bacteria known as rhizobia whereby the legume furnishes energy to the bacteria and in return the bacteria takes nitrogen from the air and converts it to a form that is useful to the plant. This occurs by the bacteria entering and colonizing a plant root where it draws nourishment from the plant while extracting nitrogen from the soil air surrounding the root hair. Species of rhizobia are specific as to the group of legumes with which they can form mutually beneficial relationships so it is very important that the correct inoculating material is used when planting various legumes. Nitrogen is directly available to the legume hosting the bacteria and becomes available to the plant community at large in a number of different ways. When legumes are consumed by grazing animals a portion of their nitrogen content is excreted by the animals in urine and to a lesser extent in manure. The percentage of this nitrogen that becomes useful to the plant community depends upon the condition of the soil surface upon which it falls and upon the amount of biological activity present in the soil. In covered soil well populated with all forms of soil life from bacteria and fungi up through earthworms and dung beetles much of the excreted nitrogen will be captured by some life form while in a bare lifeless soil most of the nitrogen will be lost to the atmosphere or to water runoff. Nitrogen also enters the nutrient cycle anytime that tissue from the legume dies and is broken down by decomposer organisms such as pill bugs, termites and fungi. There is also evidence that nitrogen can be transferred directly from legumes to other plants when the filaments of mycorrizial fungi connect the plants. The amount of nitrogen fixed by legumes varies tremendously depending upon a number of factors but in well managed pastures it can be more than enough to supply the nitrogen needs of all members of the soil-plant-animal complex. An advantage to this method of supplying nitrogen is that the nitrogen is released, as plants need it, slowly over time, being held either by living organisms or in organic matter. This prevents the bursts of nutritionally imbalanced growth seen with nitrogen fertilizers and also any significant amount of loss of nitrogen to either the atmosphere or the ground water.

Where they can grow and flourish, forage legumes can be of tremendous benefit to a grazing operation. Extension recommendations would make it seem that legumes can only be grown in areas of high rainfall on neutral to basic soils well supplied with calcium, phosphorus and potassium. It is true that these are the conditions most favorable for the growth of most legumes but good growth can often be made under less than perfect conditions, particularly if time controlled high stock density grazing is practiced. Try seeding some small plots before spending a lot of money on either seed or fertility. Look around and see what legumes are present on roadsides and other areas that have not been sprayed or fertilized and start with these species.

Do’s and Don’ts of Forage Legume Establishment and Use

1. Do not use any herbicides or nitrogen fertilizers on the areas where legumes are to be grown. Nitrogen fertilizer is toxic to the rhizobia bacteria with which legumes must form an association to fix nitrogen from the air. Also, grasses are more efficient than legumes in utilizing nitrogen so abundant soil nitrogen allows grasses to out compete and choke out legumes. Some herbicides can kill germinating small seeded legumes for several years after being applied and all herbicides reduce biodiversity and thus work against the long term best interests of graziers.
2. Soil test to be sure that sufficient calcium is present but do not add large amounts (+ 2000#) of lime at one time in an effort to raise pH as large amounts degrade both the chemistry and the biology of the soil. If phosphorus is needed, phosphorus applied as animal or green crop manure is less likely to be tied up by chemical reaction in the soil then is phosphorus from acidified rock phosphate fertilizer. Natural rock phosphates become available to higher plants slowly through the actions of soil microbes and are less likely to become tied up in unavailable compounds. Good long-term mineral nutrition comes about when the soil becomes highly biologically active. Soils with good organic content and high biological activity will be both more productive and more stable than soils with higher amounts of mineral nutrients but low soil life.
3. Inoculate each type of legume seed with the proper rhizobia bacteria before planting; seed dealers can get the proper strains of bacteria and the amount needed will be on the package. Moisten the seed with a sticker agent (milk, dilute molasses, methyl cellulose solution, etc.) that will serve to stick the bacteria medium to the seed and also provide a source of food for the bacteria when it becomes active. Stir the seed well after adding the sticker and again after adding the bacteria so that each seed is coated with the bacteria medium. Stir in a little (one cup per 50# of seed, more won’t hurt) of colloidal soft rock phosphate (the correct material is as fine as talcum powder) to provide a little phosphate in close contact to the germinating seed; do not use acidified phosphate (18-46-0, 0-46-0) as this will kill the bacteria. If too much sticker is used and the seed clumps, the excess can be taken up with more colloidal phosphate or some finely ground limestone. Keep the inoculated seed cool and in the shade as the bacteria will be killed by direct sunlight and excessive heat. If seed is not planted within forty-eight hours of being inoculated, it should be re-inoculated before planting. Different kinds of legume seed can be mixed for planting provided each is inoculated with its’ proper bacteria before mixing.
4. Do not plant too deeply; a rule of thumb is no deeper than twice the diameter of the seed. For most small seeded legumes, the ideal situation would be to have the seed setting on firm mineral soil covered only by one half inch of fine organic matter. It is hard to regulate seed depth in loose or cloddy seedbeds and these seedbeds have poor moisture retention, strive for firm fine seedbeds. In cases where shallow placement of the seed is difficult, mixing the legume seed with ryegrass and placing the mixture in a drill row can allow the grass to help the legume seed that is planted too deeply to emerge. In most cases, no-till or very low- tillage gives the best results. On established pasture, if a heavy thatch is not present, broadcasting followed by some sort of light harrow can give good results. Seeding cool season legumes in the fall after growth of the warm season grasses slows usually gives the best results where winters are not severe. Good results have been achieved by broadcasting legume seed onto frozen ground or even snow in the early spring and allowing the freeze-thaw-freeze sequence plant the seed.
5. Shade is a major concern in both establishing and maintaining legumes in mixtures with grasses. The existing grass should be grazed or mowed to a stubble height of no more than two inches for sod grasses or five inches for bunch grasses before legumes are seeded. If the existing grasses are growing vigorously, it may be advantageous to slow their growth rate by grazing or mowing to a short height and then coming back to defoliate again when two or three inches of re-growth has occurred. Be careful, this is a powerful tool that should not be over used or used when plants are in stress. Tall growing legumes such as alfalfa, sweet clover and red clover or vine formers such as vetch and Singletary peas will do better in tall growing grasses than will shorter growing legumes. If forage is stockpiled in the fall for winter grazing, to keep legumes in the mixture, the same areas should not be stockpiled every year and re-seeding may be needed on the areas stockpiled.
6. Bloat is much less of a problem on legume pastures that are grazed under time control. Bloat is most severe when animals have access to pure stands of very immature legume. If the legume is presented to the animals only after it has matured enough to have good energy to protein ratios (usually early bloom) very high percentage legume pasture can be grazed without metabolic problems. Animals do best when they are consistently grazing forage that has a narrow range of physiological age whether or not that forage contains legumes. When grazing high legume content forage, graze periods should be kept short (no more than three days with less being better) so that the stage of maturity of the forage can be controlled. It is advantageous for both bloat control and animal gains to move animals to fresh pasture in the evening after several hours of sunlight have raised the energy content of the forage. Hungry animals should not be turned to legume pasture and fewer problems and better gains will be seen when grass makes up at least forty percent of the pasture sward. There are non-bloating legumes such as arrowleaf clover and Berseem clover and including these plants in the pasture mix helps reduce the incidence of bloat. There are some animals that cannot tolerate a high legume diet and they should be removed. Bloat can also be caused, even on non-legume pasture by chemical imbalance in the soil with too high nitrogen or potassium levels being the most common culprits.
7. Don’t give up after one failure and don’t be afraid to use mixtures of legumes. All plants have preferred growing conditions as to soil type, fertility and moisture and it is common to see several different kinds of legumes each doing well on slightly different areas within one paddock. Having a variety of plants in the sward also reduces the effects of intake limiting compounds that all forages contain thus increasing forage intake and animal gains. These secondary compounds limit the amount of any one plant that animals will consume but are different for various plants and tend to cancel each others effects. Before spending a lot of money on fertility or seed, put in some small areas of different kinds of legumes; make your own “Sacrifice to the clover gods” and see what will grow under your conditions. You may find, as we did, that you would not go back to nitrogen fertilizer if it were given to you.

Characteristics of Forage Legumes

Compiled by Walt Davis 2004

1. Annual, Biannual, Perennial 7. Bloat potential High, Medium, Low, None

2. Adapted to growth zones 2..9 8. Native, Introduced

3. Warm season, Cool season 9. Potential for N fixation High, Medium, Low

4.Best growing season rain in inches 10. Preferred pH

5. Preferred soil Clay, Loam, Sand 11. Fertility requirement High, Medium, Low

6. Preferred soil Wet, Moist, Dry 12. Production potential High, Medium, Low

Characteristics of Forage Legumes

1. Annual, Biannual, Perennial 7. Bloat potential High, Medium, Low, None

2. Adapted to growth zones 2..9 8. Native, Introduced

3. Warm season, Cool season 9. Potential for N fixation High, Medium, Low

4.Best growing season rain in inches 10. Preferred pH

5. Preferred soil Clay, Loam, Sand 11. Fertility requirement High, Medium, Low

6. Preferred soil Wet, Moist, Dry 12. Production potential High, Medium, Low

Characteristics of Forage Legumes

1. Annual, Biannual, Perennial 7. Bloat potential High, Medium, Low, None

2. Adapted to growth zones 2..9 8. Native, Introduced

3. Warm season, Cool season 9. Potential for N fixation High, Medium, Low

4.Best growing season rain in inches 10. Preferred pH

5. Preferred soil Clay, Loam, Sand 11. Fertility requirement High, Medium, Low

6. Preferred soil Wet, Moist, Dry 12. Production potential High, Medium, Low

Walt Davis 2004