2003 Annual Report for GS03-024
Optimizing Forage Production and Quality Within a temperate Silvopasture System
Summary
Sustainable farms are rare in Appalachia due to severe topography, land use potential, farm size, and lack of diversification. Incorporating trees into pasture production systems may improve the economic viability of small, pasture-based farms by increasing their productivity and diversifying the product base, but their impacts on forage production and nutritive value are not well known.
In a two-year study, we have tested the impacts of trees on pasture performance with respect to forage production and nutritional value. Microclimate measures were also made for interpretation of our results.
In 1995, black walnut and honey locust seedlings were planted within 3 replicate plots of mixed pasture. A total of six plots were arranged in a completely randomized block design. Within each plot, four rows of trees were planted down a 12% slope to create increasing shade gradients both across and up the slope. Fifty-four sampling sites were established on points across the combination of tree density and slope gradients.
Sample sites were harvested about every 35 days starting from May in 2002 and 2003. Samples were dried for yield per land area, and were analyzed for acid and neutral detergent fibers, total non-structural carbohydrates (TNC), crude protein (CP), and Ca, P, Mg, and K. Microclimate measures included photosynthetically active radiation (PAR), soil temperature, and soil moisture.
Yield increases of 15% were observed with moderately spaced trees both in dry (2002) and wet (2003) growing seasons. Fiber levels were typically decreased with shade, but the levels of difference were sometimes too small to be of biological relevance. Levels of TNC were usually lower with greater tree density, while CP concentrations typically increased with shade. Mineral analyses are near completion.
Reasons for these responses are strongly linked to changes in forage microclimate. While trees reduce PAR, the reduction under medium shade was not enough to decrease forage production. Light resources were likely the limiting factor under high density trees, however. At sampling sites under low density trees, soil temperatures likely the limiting factor for production as temperatures were often above Toptimum for forage production. Soil moisture levels generally were not different across tree density or slope position treatments.
Our efforts show that appropriately spaced trees can benefit forage production in temperate pastures. The results provide an initial basis for selecting tree spacing at which forage production and quality is optimized. Future efforts will be needed to determine impact to animal health and performance, and to environmental and economic impacts.
Objectives/Performance Targets
This project had three main objectives. First, we wanted to determine the interrelationships among tree species, tree spacing, and slope on yield, botanical composition, and nutritive value of cool-season pasture. Second, we wanted to describe the silvopasture microclimate and its effects on forage quality within the tree species-spacing-slope complex. This specifically entailed measurements of light intensity and quality, soil temperature, soil moisture, and soil nutrient profile. Third, we wanted to determine the extent to which trees and pasture interact to increase total production, yield, and value from the land resource.
Accomplishments/Milestones
We have successfully measured yield and nutritional responses in forages grown under trees. Our results clearly show that forage production is increased under moderately-spaced shade trees, regardless of species. The response was similar (15% increase in yield) both in dry (2002) and wet (2003) growing seasons.
Yield of grass grown under high and low levels of shade were similar. Our measures of microclimate suggest that light is limiting under high shade, but high temperatures appear to be limiting with low shade.
The impact of shade on nutritional characteristics is not as clearly understood. Concentrations of crude protein typically increased with shade. Fiber concentrations generally were the same or lower under medium or high levels of shade compared with low shade. Shade generally reduced TNC in forage. TNC provide energy to the grazing animal, and energy is typically the most limiting factor for animal production in pastures. Thus, decreases in forage TNC may be detrimental. This may, however, be offset by the additional yield, or greater digestibility of fibers from plants grown under shade. This remains to be tested, however.
Although some production differences between tree species were observed, forage production responses generally followed the same pattern with both walnut and locust trees.
Slope had little effect on production or nutritional characteristics of forage, although tree size varied considerably with slope position. Over time this relationship would be expected to change as the tree canopies fill in more rapidly at the toe slope.
Impacts and Contributions/Outcomes
In addition to the forage measures we have made, we have been able to present data from our findings at three national meetings in 2003 and will make an additional three presentations at national meetings in 2004. We anticipate publication of three refereed journal articles based on this work and anticipate publication of one to two refereed reviews.
Perhaps as powerful as publication was our discussion of agroforestry practices with extension agents at the Virginia Cooperative Extension In-Service-Training sessions in March of 2004. Several new and challenging ideas were presented. In addition to discussion of incorporating multiple agroforestry enterprises into a farm, agents were presented with the concept of a 60-yr production cycles (to include tree harvest), and the economic consequences of these activities. A lot of rumbling occurred throughout the talk as the agents were stretched beyond their normal production paradigms.