Optimizing Forage Production and Quality Within a temperate Silvopasture System

View the project final report

• 2003 annual report

Commodities

• Nuts: walnuts
• Additional Plants: trees

Practices

• Crop Production: agroforestry
• Production Systems: general crop production

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, non-structural carbohydrates, crude protein, 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 often increased with shade. Lower CP in forage from open sites would be due to dilution effect. Concentrations of Ca typically increased with high tree density, but other mineral responses to treatments were complex and less consistent.
Reasons for yield and nutritional responses appear strongly linked to changes in forage microclimate. While shade from trees reduces incident light, the reduction in PAR under under medium shade was also accompanied by reduced soil temperatures, creating a better growing environment for the forage crop. Light resources were likely the limiting factor under high density trees, however. At sampling sites under low density trees, soil temperatures appear the limiting factor for forage production as temperatures were often above Toptimum for cool season forages. 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.

Introduction

Producers and researchers continue to strive for higher productivity levels by developing and improving agricultural technology including genetics, machinery, fertilization, and pesticides. However, such strategies may not address the needs for long-term productivity or sustainability of our production systems and in some cases may mask or even contribute to environmental contamination and degradation resulting from agrochemical pollution, soil erosion, pest problems, and loss of biological diversity. In short, the current methods of increasing productivity may come at high environmental cost and may not be sustainable.
Agroforestry may provide alternatives to using capital inputs for increasing production. Agroforestry practices have potential to optimize positive biological interactions between crop components and emphasize species diversity rather than only crop yield.
Silvopastoral practitioners intentionally integrate trees, forage crops, and livestock to reap the benefits of their interactions. Greater forage production, nutritive value, and digestibility are reported for pastures grown under trees relative to open sites, and this may reflect changes in botanical composition.
Potential tree species for the Appalachian region include black walnut and honey locust. Black walnut produces both high value wood and generates an annual nut crop; management for either or both outputs is possible. Honey locust is of interest because selected varieties (e.g. ‘Millwood’) can produce high-energy pods that potentially can serve as a valuable fodder source. The pulpy pods may contain up to 35%, and yields are similar to an equivalent acreage of oats.
Despite the potential benefits of silvopastoral practices, very little research has been conducted in the humid, temperate regions of eastern North America. Design and management of silvopasture systems will vary by location and, it is important to test tree impacts on forage production systems on a regional scale before making widespread recommendations to farmers.

Our objectives were to determine the interrelationships among tree species, tree spacing, and slope on yield, botanical composition, and nutritive value of cool-season pasture. Further, we wanted to describe the silvopasture microclimate and its effects on forages 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.