Tall Fescue Online Monograph

Fertilizer is the largest annual expense for most forage programs. To reduce this expense without sacrificing yield or forage quality, tall fescue pastures may be interseeded with legumes, such as clovers (Trifolium spp.). Legumes grow with bacteria (Rhizobium or Bradyrhizobium spp.) in a symbiotic relationship by forming N-containing nodules attached to their roots. The bacteria convert gaseous N from the atmosphere into a form that they, along with the associated grass plants, can use. Research has shown that adding legumes can improve tall fescue pastures and hayfields in several ways.

The presence of a good stand of legumes with tall fescue eliminates the need for spring N applications. Research in many geographic areas has shown that legumes grown with tall fescue can produce the same yield as tall fescue fertilized with 67 to 168 kg N/ha (60-150 lb/acre), depending on the legume used (Hoveland et al., 1986; Matches, 1979).

Legumes also help extend the grazing season farther into the summer (Fig. 6-10). For example, two-thirds of the growth of a tall fescue-red clover (T. pratense L.) mixture is produced after the first harvest, compared to only one-third for tall fescue fertilized with 67 kg N/ha (60 lb N/per acre). The presence of the legume leads to a more evenly distributed forage supply for grazing (Fig. 6-9), thus reducing the large swings in over- and underproduction that occur with pure tall fescue stands. Legumes can also improve the protein and energy content of a pasture or hayfield, leading to improved animal performance. They can also reduce the negative impact of fescue toxicosis (see Chapter 16).

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Fig. 6-9. Typical growth curve of tall fescue (line) grown with red clover (dot-dash line).		Fig. 6-10. Beef cattle grazing a tall fescue-red clover mixture in summer. Photo by Garry Lacefield.

Selecting the Proper Legume Species

Many different legumes can be grown successfully with tall fescue. Alfalfa (Medicago spp.), red clover, white clover (T. repens L.), birdsfoot trefoil (Lotus corniculatus L.), and annual lespedezas {Kobe [Kummerowia striata var. kobe hort. (= Kummerowia striata (Thunb.) Schindl.)] and Korean [Kummerowia stipulacea (Maxim.) Makino]} are examples. Selecting the appropriate legumes depends on the environmental conditions of the area, soil type and fertility, intended use of forage, and management capabilities of the producer or manager.

Often the factor that is most limiting in legume use is successful establishment. A young legume seedling must develop its root system and capture sunlight for photosynthesis before being shaded and outgrown by the established tall fescue plants. Because of these difficult competitive conditions, those legumes deemed most successful are those with high seedling vigor. That is the primary reason why white and red clovers are the most widely used legumes in tall fescue pastures.

To obtain stands of red and white clovers established in tall fescue, several important practices must be followed. White clover should be seeded at rates of 1 to 3 kg/ha (1-2.7 lb/acre) and red clover at 4 to 8 kg/ha (3.6-7.2 lb/acre); both should be inoculated with the appropriate strain of live Rhizobium. Care should be taken to use inoculum that has not been stored at high ambient temperatures or exposed to sunlight. Best times for seeding are October to November or mid February to early March, preferably shortly before an imminent rain. Late winter seedings have proved successful, since tall fescue is dormant at that time and does not provide much competition to the clover seedlings.

Legume seed can be drilled or broadcast. If the stubble is no taller than 5 cm (2 in) and the tall fescue is dormant, broadcasting is preferred. If the stubble is high or the tall fescue is beginning to grow, a no-till drill should be used to cut the existing sod surface so that the seed is placed in contact with the soil (see Chapter 5).

The seed should be placed no more than 5 to 7 mm (0.25 in) deep. Deeper seed placements will result in delayed emergence or possible failure. When a no-till drill is used, the depth of seed placement should be checked carefully because changes in soil moisture or condition since the last use may alter the actual seeding depth. In general, because of the sensitivity of clover seed to seeding depth, broadcast seeding is preferable to planting the seed too deeply. This is especially important for species such as white clover that have small seed.