Agroforestry Research Unit

Agroforestry systems have the potential to sequester carbon in wood and soil, making them a sink for atmospheric carbon dioxide (CO2).  Carbon sequestration is a mitigation strategy to remove CO2 from the atmosphere.  Moreover, agroforestry systems can introduce native tree species and warm-season grasses, reducing the need for additional nitrogen fertilizers.  This also limits the potential emission of nitrous oxide (N2O), a potent greenhouse gas, strengthening the climate change mitigation effect.

Agroforestry systems may be less susceptible than conventional agricultural systems to adverse weather events, such as heatwaves and floods.  Trees can create microclimates that benefit the well-being of livestock in silvopasture systems.  Native forages and trees have proven to be more resistant to flooding, and ensure the continuation of production and ecosystem services even after these otherwise disastrous events.  By selecting native tree and grass species, agroforestry can increase the overall resilience of production systems for timber, forage, and livestock simultaneously.

Silvopasture is the integration of trees and forages into a working system on a farm.  A silvopasture is one form of agroforestry.

Silvopastures are intentional and considered an intensive form of on-farm management for timber production, fruits and seeds, forage products, livestock production and husbandry, and/or wildlife habitat.

Well-managed silvopastures:

  1. Employ agronomic principals using a variety of introduced or native forages;
  2. Provide reasonable nutrient inputs and nitrogen-fixing legumes to foster fertility;
  3. Utilize rotational stocking approaches and other top grazing management principles to optimize forage utilization and ecological well-being of soil, water, air, and biological resources on the farm.

What type of research is being conducted?

Native warm season grasses are grown in alleys between lines of trees on 17 acres of bottomland near the Neuse River.  The grasses are a mixture of switchgrass, big bluestem, Indiangrass, and eastern gamagrass.  The trees are loblolly pine, longleaf pine, and cherrybark oak.  The forage treatments are:

  1. Rotational grazing with Angus cattle
  2. Cutting grass for hay twice per year
  3. Cutting grass for hay once per year
  4. Cutting the grass for biofuel harvest once per year
  5. Leaving the grass for conservation

How are systems being evaluated?

  • Cattle gain, temperature, and fly counts are being determined on two herds: one under the silvopasture and one in open pasture with the same forage mixture
  • Tree survival and growth
  • Forage production and quality
  • Soil health via organic matter and nutrient properties over time

When was the research initiated?

Dr. Paul Mueller initiated the experiment in 2007 with the planting of bare root tree seedlings in a previously cropped field.  Tree seedlings of loblolly pine, longleaf pine, and cherrybark oak were planted in five lines on 17 acres.  Lines of trees were composed of triplicate sets spaced at 7 foot apart.  Lines of trees were separated by 40-foot and 80-foot alleys for testing of tree density.  Corn and soybean were grown for the first six years, followed by one year of ryegrass cut for baleage, and then planting of native warm season grasses.

What research results have been found so far?

Economic evaluation of alley-cropping

  • Corn and soybean production were low during the first four years of management due to droughts and floods
  • Tree survival and growth rates were good and suggested that strategically planted trees on this marginal cropland were adding value to a farm operation
  • Projected economic returns were 2 to 7% based on growth rate of trees

Source: Cubbage, F.W., Glenn, V., Mueller, J.P., Robison, D., Myers, R.¸ Luginbuhl, J.-M., & Myers, R. (2011). Early tree growth, crop yields and estimated returns for an agroforestry trial in Goldsboro, North Carolina. Agroforestry Systems, 86, 323-334.

Greenhouse gas emissions under alley-cropping

  • Soil nitrous oxide (N2O) emission was mitigated by the presence of trees in the agroforestry design
  • Tree canopy after 8 years of growth led to lower soil temperature and soil water content, which helped to reduce N2O and carbon dioxide (CO2) emissions
  • Data suggest that environmental sustainability of marginal croplands in the southeastern US can be improved with agroforestry systems

Source: Franzluebbers, A.J., Chappell, J.C., Shi, W., & Cubbage, F.W. (2017). Greenhouse gas emissions in an agroforestry system of the southeastern USA. Nutrient Cycling in Agroecosystems, 108, 85-100.

Spatial variation in soil properties

  • Soil texture and soil organic matter were determined at specific points in the field and maps were created across the field
  • Near-infrared spectroscopy was appropriate for predicting soil texture and organic matter
  • Soil texture was predicted with greater precision than soil organic carbon fractions

Source: Deiss, L., Franzluebbers, A.J., & Moraes, A. (2017). Soil texture and organic carbon fractions predicted from near-infrared spectroscopy and geostatistics. Soil Science Society of America Journal, 81, 1222-1234.

Soil organic carbon fractions

  • Total, mineral-associated, and mineralizable carbon fractions varied along a soil texture gradient
  • Soil organic carbon fractions were positively associated with surface area and iron hydroxides
  • Mineralizable carbon had the most complex relationship with clay concentration

Source: Deiss, L., Franzluebbers, A.J., Amoozegar, A., Hesterberg, D., Polizzotto, M., & Cubbage, F.W. (2017). Soil carbon fractions from an alluvial soil texture gradient in North Carolina. Soil Science Society of America Journal, 81, 1096-1106.

Microclimate of silvopastures

  • Native warm-season grasses were successfully established under disk and no-till in areas under the trees and open-pastures.
  • Forage production and quality were not affected by tree species.
  • Microclimate under the trees vs. open-pasture varied as a function of time of day and month of the year, and it was moderately altered during the summer.

Source: Castillo, M.S., Tiezzi, F., & Franzluebbers, A.J. (2020). Tree species effects on understory forage productivity and microclimate in a silvopasture of the southeastern USA. Agriculture, Ecosystems and Environment, 295, 106917.

What is the biggest environmental limitation?

Flooding due to proximity to the Neuse River is a continual threat.  Flooding of the site has occurred in July 2013, October 2016, spring 2018, and September 2018.

We have seen great resilience in the native warm-season grasses and all native trees to these flooding events.  Water was ~2-foot high over the site for several days during some of these events.

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