Grazing School

Workshops

Research

Faculty

News

Weather

Contact us

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 10, No. 2

Introduction: Increasing plant species diversity in pastures has been shown to provide more even forage yield distribution and quality through the grazing season (Forage Systems Update, January 1, 2000:Vol 9, no. 1). A key question facing graziers is the stability of such diverse plant communities. If a complex mixture is sown, what will remain in the pasture in later years? The same question can be asked for monocultures and simple mixtures. Five years after sowing a pasture, will the plant community be representative of what was sown? One objective of the diversity study at FSRC which we have reported on previously is to determine changes in composition of pasture mixtures seeded with different levels of species diversity over time with management-intensive grazing (MiG).

Material and Methods: Sixteen grass or grass-legume mixtures were established in 50 ft X 50 ft plots in a completely randomized design with four replications. Mixtures varied in degree of species complexity. Seven mixtures were tall fescue based (TF), seven mixtures were smooth bromegrass based (SB), and two contained both TF and SB along with either five or six additional species. Grass components were broadcast seeded on September 5, 1994 on a prepared seed bed and rolled with a cultipacker. Legume components and big bluestem (BB) were frost seeded on March 10, 1995. Red clover (RC) and birdsfoot trefoil (BFT) establishment with frost seeding was very good while alfalfa (Alf) and big bluestem establishment were poor. Legumes were seeded first as binary mixtures with each base grass and then in combination with one another within each base grass. More complex mixtures were created by adding orchardgrass (OG), timothy (Tim) and big bluestem to the base grass+ 3-legume mixtures. Thus, mixtures included 1,2,3,4,6,7, or 8 species. Each mixture was formulated to provide 80 seeds/sq-ft with the base grass always providing 50% of the seed in mixtures and all other components being equally represented. The exception was the eight species mix where all components were allocated in equal amounts. In the discussion, mixtures containing four or fewer seeded species are classified as simple mixtures while those containing six to eight are classified as complex mixtures. Simple mixtures contain only one seeded grass.

Swards were uniformly managed to encourage establishment during the 1995 growing season and were mechanically harvested in 1996 and 1997. Tall fescue and smooth bromegrass monocultures received 120 lb N/acre annually as three 40-lb applications applied in March, June, and September. Phosphorus and potassium fertilizer (0-40-80) were applied equally to all plots each September.

In 1998, 1999, and 2000, 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 1999 and 2000 measurements were made every 4 weeks regardless of regrowth stage from April through October. Species composition is reported as yearly means.

Hits were recorded on individual species basis except that all non-seeded forbs were grouped as broadleaf weeds and the less desirable non-seeded grasses and grass-like plants were grouped as grassy weeds, while hits on bare soil, surface litter, and manure were recorded separately but grouped together as non-vegetation hits. All desirable forage species, broadleaf weeds, and grassy weeds constituted vegetation hits. Basal cover of individual species was calculated as the number of hits for that species divided by total hits. Percent basal cover by seeded species as shown in Figure 3 is the percentage of forage cover represented by seeded species, not the percentage of total hits.

Species composition was analyzed using the SAS General Linear Models procedure using separate models for mixture effect, base grass effect, and number of species in the mixture effect. Least square means were calculated and significant differences determined using protected least significant difference procedure.

Results and Discussion: There were significant differences among the individual pasture mixtures for basal cover of forage species and seeded species, but not for total vegetation in 1998 (Y1). In 2000 (Y3), total vegetation, forage cover, and seeded species were all significantly different for individual mixtures. In SB-based pastures, forage cover and seeded species cover in 1998 were slightly less than TF or TF+SB-based pastures . This is probably due to slower rate of establishment by SB compared to TF. At the beginning of the study SB-based pastures had more non-vegetative cover and more weeds than TF-based pastures. By the third year of grazing, TF, SB, and mix-based pastures all had similar forage cover, but were significantly different in basal cover of seeded species and seeded species as a percent of total forage cover. In 2000, SB based pastures had only 38% basal cover as seeded species while mixed and TF-based pastures had 66% and 51%, respectively. Even when rest periods were extended to accommodate the needs of SB, persistence of SB under grazing in this environment is poor.

Pastures were in their fourth year of growth when grazing began. Plots had been mechanically harvested uniformly in the three preceding years. At the beginning of grazing, total forage cover was approximately 60% for all mixtures (Figure 1). Total forage cover increased through the years of grazing and was between 75% and 85% by the third year, with monoculture and simple mixtures being significantly lower in forage cover than the mixtures containing six or eight species. In the simple mixtures, most of the increase in forage cover came from non-seeded species including Kentucky bluegrass, white clover, annual lespedeza, and crabgrass. The relatively low forage cover at the beginning of the study illustrates what happens to pastures when they are hayed or in other non-grazing uses, such as CRP. Stand thinning occurs as grazing pressure is reduced due to excess shading.

Basal cover of seeded species declined or remained the same for simple mixtures from Y1 to Y3, while significantly increasing for complex mixtures during the same time period (Figure 2). This difference may be due to more microenvironment flexibility for complex mixtures compared to simple mixtures. Microsite variances in soil fertility, compaction, and drainage can be very large in grazed pastures as a result of animal grazing habits, excretion, and travel patterns. A monoculture or simple mixture may not provide a range in microsite adaptation characteristics that a more complex mixture might exhibit.

The percentage of total forage cover by seeded species remained unchanged from Y1 to Y3 for complex mixtures while declining significantly during the same period for monocultures and simple mixtures (Figure 3). The greatest decline occurred in SB-based pastures as the SB contribution fell from 29% to 22% during the three-year period. These results suggest that more complex mixtures are more stable over time than are simple mixtures with management-intensive grazing.

While the total cover by seeded species in the complex mixtures changed little over the three years of the study, contribution by individual species in the mixture did change (Figure 4). Based on equal number of seeds being sown for each component, the mixture should have, theoretically, 12.5% basal cover by each component species . In 1998, only red clover had significantly greater than 12.5% cover. Red clover is a very aggressive legume and thrives in the north Missouri. Orchardgrass, alfalfa, and big bluestem were significantly below 12.5%. By Y3, tall fescue and birdsfoot trefoil had increased above the component equality level. The tall fescue-birdsfoot trefoil mixture is one of the top yielding mixtures in this study. Red clover, while declining significantly from its Y1 level, remained above the balance point. Over the three years of the study, orchardgrass increased to reach balance level while timothy fell from 12.5% to 5%. Alfalfa remained unchanged and big bluestem, while increasing significantly from Y1 to Y3, remained a minor component of the pasture.

Results indicate that complex pasture mixtures can be sown and maintained as a complex mixture with management-intensive grazing. Simple mixtures are prone to invasion by other common indigenous forage species. While total forage cover may be similar for the planned mixture and the invasive mixture, forage yield and distribution may be more easily manipulated in the planned mixture.

Site maintained by people at AgEBB
agebb@missouri.edu