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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email: DavisDK@missouri.edu

Forage Systems Update
Vol 11, No. 4

For the past twenty years, most of the pastures at FSRC have been managed as grass-legume mixtures with very little annual input of nitrogen fertilizer. When we make recommendations to producers to switch from N-based to legume based pastures two common concerns are the relative yield of grass-legume mixtures compared to N-fertilized pastures and what is the reliability of legumes from year to year. A third less commonly asked. but of equal importance, question is the relative cost of production. In several previous issues we have featured different aspects of our pasture diversity study. We have completed five years of grazing on these plots and can begin to evaluate some of these common questions.

While the study includes 16 pasture mixtures of different complexity, this report will only be looking at the simplest mixtures to evaluate the role and behavior of red clover and birdsfoot trefoil in tall fescue pastures. The four treatments being compared are tall fescue + 80 lb N/acre (TF+N), tall fescue with no seeded legume or N (TF-0), tall fescue + red clover (TF+RC), and tall fescue + birdsfoot trefoil (TF+BFT). Grass was seeded in September, 1994, and the legumes were frost seeded in March, 1995. There has been no additional interseeding since the original planting. Any legume regeneration has come by way of natural reseeding. The pastures are maintained at a medium soil test level with target pH of 6, P1 of 20 lb/acre, and exchangeable K of 200 lb/acre. Soil tests taken in 2001 did not meet these targets and 0- 60-250 was applied in September, 2001.

In each year from 1998 through 2002, individual plots were grazed whenever a particular plot reached 8 to 10-in. mean sward height. Plots were grazed with six to eight steers for four to seven hours to remove approximately 50% of the forage biomass. Basal cover of species composition was determined by step-point method with 100 points recorded for each plot. In 1998 stand measurements were made prior to each grazing event while in subsequent years measurements were made approximately every 4 weeks regardless of regrowth stage from April through October.

Trend lines for red clover and birdsfoot trefoil cover were determined using linear regression as first, second, and third order models with best-fit model reported . Variability was calculated as standard deviation divided by the sample mean. Variability is simply a measurement of year to year change in presence of that species in the mixture. Low variability means greater predictability of pasture performance and, hence, greater reliability across a range of weather conditions. We looked at these two legumes both as seeded and invader species.

Results and discussion: Variations in pasture yield among the four mixtures occurred each year, but not in a consistent manner. Year to year variations in forage yield can be attributed to rainfall variations, but also to species composition. Forage yield was significantly lower in 1999 and 2000 when growing season rainfall was substantially lower than normal. The TF+N pasture had significantly higher forage yield two out of five years compared to the other mixtures. In 1998, 1999, and 2000, forage yield of TF+BFT was not significantly different from TF+N. (Figure 1). In four out of five years, TF+0 yielded significantly less than all other mixtures. It is inevitable that there will be pasture yield variations from year to year. We are interested in understanding why variations occur and what we can do to minimize those variations.

Figure 1. Five-year mean yield for four pasture mixtures with hashed bars indicating mean of all four mixtures for that year

This value describes how much annual variation can be expected in forage yield of a particular mixture. It is a mathematical description of what Figure 1 suggests visually. The greatest amount of annual variance occurs in tall fescue-red clover mixtures and the least occurs in tall fescue-birdsfoot trefoil mixtures. The letter(s) following each value indicate which variability indices are significantly different.

These results indicate that either tall fescue with N fertilization or tall fescue with birdsfoot trefoil are the most reliable pastures across a range in rainfall conditions. Birdsfoot trefoil is plagued with a wide range of root and crown diseases in the humid Midwestern environment so it may be surprising to some that it is such a stable mixture. The key is in its ability to naturally reseed itself. The higher rate of variability in red clover is a reflection of its lesser ability for natural reseeding without extended rest periods. In this study with a target grazing height of 8 to 10 inches, red clover was not adequately rested to allow reseeding. So the key factor is stand persistence, not individual plant persistence.

We also looked at variations in the species composition of the mixtures over the five year period.

Figure 2. The trend line for birdsfoot trefoil indicates only minor changes over time.

The relatively low variance in birdsfoot trefoil stand density is consistent with the forage yield data reported above. One of the advantages frequently cited for birdsfoot trefoil is that it can tolerate both excessively dry and excessively wet soils and seasons. These are characteristics that would help minimize seasonal and site variations. The drier conditions experienced in 1999 and 2000 may have reduced the competitiveness of companion species allowing trefoil to flourish.

Figure 3. The trend for red clover exhibits a much wider annual variation in stand density.

Another piece of data that was collected in some, but not all years were legume seedling counts taken in May. In 1999 very few seedlings were counted while in 2000 a relatively high number of seedlings were found. In 1998 the mean rest period for TF+RC pastures was 31 days while in the much drier 1999 season, mean rest period was 46 days. The opportunity for reseeding was much greater in 1999 than it was in 1998. Factors like these combined with seasonal weather variations tend to make red clover more cyclic in its presence and yield contribution in pasture.

Figure 4. The trend line for birdsfoot trefoil indicates a more aggressive invader habit than red clover.

The TF+0 treatment did not have either red clover or trefoil seeded in the pasture but has been invaded over time by both species (Figure 4). Comparing the trend lines for the two species, we see that birdsfoot trefoil has a much stronger colonizing ability than does red clover. Red clover continued to exhibit its cyclic habit while trefoil showed a steady increase in stand density.

The practical way to reduce the cyclic nature of red clover is to overseed on a regular basis. Recommendations range from annually to every three years. Annual overseeding with about four pounds of red clover can make red clover much more consistent and reliable. Avoiding overgrazing and allowing periodic rest of birdsfoot trefoil appears to be adequate for stand maintenance making overseeding unnecessary once a stand has been established.

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