Understanding Plant-Soil-Livestock Interactions: A Key to Enhanced Sustainability in Southern-Pine Silvopasture Systems

Understanding Plant-Soil-Livestock Interactions: A Key to Enhanced Sustainability in Southern-Pine Silvopasture Systems

Summary

In May, species composition measurements at Americus determined that canopy cover of crimson clover was approximately 15% in both bahiagrass (Paspalum dilitatum) silvopasture and open-pastures. There were no shoot biomass yield differences as a result of spatial comparisons (1 m from tree centers in lane vs lane middle) in May however, clover-treatments had a significantly higher biomass yield by 28% in clover- versus comparable N-fertilizer treatment paddocks. No differences in shoot biomass yield were detected in July however, in the silvopastures in August, there was a significant 10% reduction in biomass yield at sampling points closest to the trees versus the lane middles. No treatment or spatial differences were found in percent water-stable aggregates (%WSA) however, there was a significant temporal difference as %WSA increased overall by 23% in August versus June. Soil strength (J/m2) increased with depth however, sample sites closest to the trees showed a 50, 56 and 43% reduction in soil strength at 5, 10 and 15 cm, respectively. When 17 individual forage species were compared to a no-plant control in soil from the Americus site under greenhouse conditions, 3 of the forages had a significantly positive effect on percent water-stable soil aggregates while 4 of the forages significantly reduced percent water-stable soil aggregates.

Objectives/Performance Targets

Objectives

1. Determine the impacts of N supply (fertilization versus clover) on above- and below-ground forage productivity, forage quality and plant diversity in developing silvopasture.
2. Determine the impacts of N supply on pasture soil structural stability and relationships to soil compaction, and water infiltration and retention in developing and mature silvopasture.
3. Compare the use of small ruminants to the more conventional use of herbicides to control invasive broadleaf plants within developing silvopasture systems and impacts on infiltration.
4. Examine the economic feasibility and level of landowner acceptance of management practices being proposed.
5. Estimate effects of silvopasture management practices on watershed-level hydrology using the Hydrology Simulation Program-Fortran (HSPF).

Accomplishments/Milestones

At Americus, a successful stand of ‘Dixie’ crimson clover (Trifolium incarnatum) was obtained from the October 2004 planting; clover was sown at Andalusia in October 2005. Pastures at Americus, Andalusia, and Chipley had been sampled in March for fertilization requirements. Fertilizer was applied according to soil test recommendations in May; no fertilizer N was added to the clover treatment plots. Soil samples were collected at full clover bloom in May and again in early August at two points on 5 separate transects positioned perpendicular to the tree strips in each silvopasture and in a similar configuration in the open-pasture paddocks at Americus. On each transect, one sample site was located 1 m from the center of the tree base and the other at the midpoint between adjacent sets of tree strips. In May and August, the samples were analyzed to characterize percent water-stable aggregates (aggregate stability); soil compaction was measured in situ at 5-cm increments to 20 cm in July. In August, 15-cm soil cores were collected to characterize root biomass. Shoot biomass above 5 cm was clipped from 10 0.25-m2 quadrats in each paddock along transects at points used for soil sampling in May, July and August. All paddocks at Americus were fenced and water installed in June 2005. In September, vegetation was characterized at 6000 points each for understory and overstory at the woodlot set for use at the Fort Valley site. The Fort Valley site will be fenced in late April 2006 and water installed; grazing with goats will begin in May 2006. Portable weather stations were assembled and located in silvopasture and open pasture at Americus (5-yr old Pinus palustrus)and Chipley FL (20-yr old Pinus taeda)and launched in early November 2005. The first greenhouse study was greenhouse study was planted August 12 and completed December 22, 2005. The second greenhouse study will be planted in August 2006. Soil compaction and percent water-stable aggregates were chatracterized in silvopasture sites at Fort Valley in September, Chipley in November and at Andalusia in December.
In June 2005, producer field days were planned for spring and summer 2006: Owens Farm, Chipley FL April 5, 2006; Evans Farm, Jakin GA June 15, 2006; JCPMC, Americus GA July 27. Additional producer field days will be planned in June 2006 for Solon Dixon Forestry Education Center, Andalusia AL and Fort Valley State University in Fall 2006. An MS animal science student was recruited for the project in March 2006 and will begin Summer Semester 2006. Planning for 4 producer training sessions to be held in 2007 will begin in June 2006. Preliminary results for the hydrologic modeling will be completed in June 2006.

Impacts and Contributions/Outcomes

Through evaluation of management strategies designed to maintain both pasture productivity and soil health (quality), results from this project will provide understanding that will allow Southern Region producers to move more profitably toward conversion of perennial pastures to silvopasture and sustainable long-term use for several ruminant livestock production options.

Collaborators: