Silvopastures integrate trees, forages, and livestock. Tall fescue, the dominant forage in much of the U.S., harbors an endophyte that produces toxic ergot alkaloids. Diluting the sward with other forages can reduce ergot alkaloid concentrations, but it is unknown how shade impacts alkaloid production and productivity of different forage mixtures. This study tested the effects of increasing shade and mixture complexity on sward yield, botanical composition, nutritive characteristics and ergot alkaloid concentrations. Slatted shade structures created 30, 50, and 70% shade compared to full sun. Three forage mixtures were evaluated (SIMPLE = tall fescue and white clover; INTERMEDIATE = SIMPLE + orchardgrass and red clover; and COMPLEX = INTERMEDIATE + Kentucky bluegrass, birdsfoot trefoil, and alfalfa).
Fifty and 70% shade reduced yield while red clover and orchardgrass dominated shaded swards. Birdsfoot trefoil, Kentucky bluegrass, and white clover did not perform well in any treatment. Nutritive value declined beneath shade in spring and fall. Sward ergot alkaloid concentration increased beneath shade in simple mixtures because of greater proportions of tall fescue. In the intermediate and complex mixtures, ergot alkaloids were diluted by other forage species and was not affected by shade. This illustrates the importance of incorporating multiple species into the sward. Low light levels may not have been sufficient to meet the forages’ high energetic demands in the spring. Even though total forage production or nutritive value may be sacrificed during part of the year, this may be compensated for by diverse swards diluting ergot alkaloid concentrations.
- To compare the response of forage species mixtures to different shade levels. Measures of interest include: a. Biomass production b. Species composition c. Nutritive value (protein and fiber concentrations), and d. Ergot alkaloid concentrations
- To present data on our findings to researchers, technical service providers, and producers interested in forage-livestock system management in the fescue belt
A replicated small plot study was established at Virginia Tech’s Southern Piedmont Agricultural Research and Extension Center (SPAREC) near Blackstone, VA. The study used a randomized complete block design (four replications) with a factorial treatment arrangement to test the effects of four shade levels (0%, 25%, 50%, and 75% shade) on three forage mixtures of varying complexity (simple = tall fescue & white clover; intermediate = simple + orchardgrass & red clover; and complex = intermediate + Kentucky bluegrass, alfalfa, & birdsfoot trefoil).
All of the species used are cool-season (C3) forages that are light saturated at approximately 50% of full sunlight. That is, an individual C3 leaf can only utilize about half of the photosynthetically active radiation that would be available for photosynthesis on a bright, sunny day. Thus, some reductions in light may not negatively affect photosynthesis, and the lower air and soil temperatures caused by shading can benefit C3 species by reducing heat stress and water loss through evapotranspiration.
Shade structures were used in this experiment to achieve greater control over available light levels. The structures are similar to those used by Varella et al. (2001) who reported that slats placed on a frame could be used to create the mottled light patterns and shaded environments similar to that found in silvopastures. Slatted snow fence was secured to the top and sides of an elevated frame to achieve approximately 50% shade. Half of the slats were removed from the fence to achieve approximately 25% shade, while shade cloth was added to the 50% treatment to achieve approximately 75% shade. (Shade cloth was used in this case because it was not feasible to add slats to the snow fence.) Shade structures measured 8′ x 16′ which is more than adequate to cover the 8′ x 10′ plots for the majority of the day.
In April 2015, plots were seeded into a conventional seedbed using a small plot cultipack-type seeder. Shade structures were placed over plots immediately following seeding. Plots were harvested for yield when the forage reached an average height of 15”. A self-propelled small plot forage harvester was used to clip and weigh a 5′ x 10′ strip through the center of each plot. Plots were harvested twice during 2015 and five times in 2016.
At each harvest, three 250-g subsamples were collected from each plot. One subsample was weighed, dried at 60°C for 3 days, then weighed again to determine dry matter and used to calculate plot yields. Subsamples were ground to pass a 2 and 1-mm screen using Wiley and Cyclone mills, respectively. Ground samples were scanned with a near infrared spectrophotometer (NIRS) and a robust NIRS equation developed for fresh hay and forage was used to estimate sample nutritive value. The second subsample was hand-separated into weeds and individual forage species components. Once separated, each component was oven dried as previously described, and the dry weights were used to calculate the relative contribution of each component to overall yield. The third subsample was collected, immediately frozen, freeze dried, ground following the above procedures, and analyzed at Agrinostics Ltd. (Watkinsville, GA) to quantify total ergot alkaloid concentration using a Phytoscreen PT ergot alkaloid kit.
Yield was reduced at 50 and 70% shade, and showed no difference between mixtures, regardless of forage diversity. During spring and fall, seasonal yields were reduced beneath shade, but intermediate and simple mixture yields were increased at 30% shade during summer once forages were established. Most likely, this occurred due to reduced irradiance during the periods where cool-season species need the most resources to sustain high growth rates, whereas during the hottest part of the year when cool-season forage growth is reduced, shade tolerant species thrived and remained vegetative under the modified microclimate of the 30% shade treatment. During this time even intermediate mixtures under 50% shade yielded as much as open sun counterparts. Once forages established, orchardgrass increased while weeds and white clover decreased in intermediate and complex mixtures. Red clover also comprised a significant proportion of the swards beneath shade. In the simple mixtures, tall fescue increased under shade while white clover decreased. Although orchardgrass is not particularly well-adapted to Virginia, silvopastures may be an effective way to integrate this and other marginally adapted cool-season grasses into grazing systems.
Nutritive value declined beneath shade in spring and fall, most likely because the filtered light could not supply enough energy to meet the rapid growth rates of cool-season forages during these times. Crude protein was high enough to meet metabolic requirements for dry and lactating cows, and steers. However, during the summer steers may need energy supplementation in order to attain acceptable production goals. Total sward ergot alkaloid concentration was elevated beneath shade in the simple mixtures because of greater proportions of tall fescue. In the intermediate and complex mixtures, fescue was diluted with other forage species and ergot alkaloid concentration was minimally affected by shade. This illustrates the importance of incorporating multiple species into the sward to dilute the alkaloid concentration.
Educational & Outreach Activities
Preliminary findings have already been shared with producers, students, and agricultural professionals at the American Forage and Grassland Council’s annual meetings in 2016 and 2017, Virginia Tech’s Crop and Environmental Sciences/Horticulture Graduate Research Symposium, numerous local field days and tours, Virginia Tech’s Forage Crop Ecology class, Virginia Tech’s first “Agroforestry Convergence” meeting, the World Congress of Silvo-Pastoral Systems held in Portugal in 2016, and the National Small Farms Conference in 2016. One manuscript has been submitted for publication in Agroforestry Systems, and another is being prepared for submission into Crop Science.
This project has shown that well managed silvopastures can indeed produce as high quality and quantity of forages as traditional open pasture systems. Furthermore, ergot alkaloid concentrations at the sward level can be reduced by incorporating multiple forage species into the sward, something that hadn’t been looked at in shaded environments.
Silvopastures have the capacity to greatly improve resource use efficiency and increase production on a per land unit
basis, often with reduced inputs (Nair, 1993). Along with improving productivity, silvopastures can enhance many
ecosystem services including water quality (by reducing runoff and increasing infiltration and groundwater recharge),
nutrient cycling, biodiversity, and wildlife habitat (Shrestha and Alavalapati, 2004; Nair 1993). Improving animal
performance and forage productivity and/or quality in these systems can support increased annual revenues. With
the potential to reduce the effects of fescue toxicosis, silvopastures in the Upper South would allow producers to
have healthier livestock and a more profitable enterprise. Silvopastures can also enhance a farm’s aesthetic value which is a benefit not only to the landowner but to the community as a whole (Shrestha and Alavalapati, 2004).
This project has given us valuable insight into how to better manage silvopastures to ensure sustainability in these types of systems in regards to both forage quantity and quality. This study resulted in some outcomes that we were not expecting, which reiterates the idea that science doesn’t always go as planned, and there is always more to learn.