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

Results from the three-year study of forage-soil relationships in developing longleaf pine-bahiagrass silvopasture on Coastal Plain soil at Americus GA indicate that forage productivity and quality can be enhanced, and N fertilizer additions replaced by introduction and maintenance of legumes. Results also support the beneficial effect of legume presence for soil quality (aggregate stability). Spatial differences in both forage productivity and soil quality (penetration resistance) were detected in silvopasture alleys positions relative to trees. Observations of cattle behavior in mature silvopasture versus open pasture in March, June and September at the Owen Farm in Chipley FL indicated that cattle spend significantly more time grazing in a slivopasture versus open pasture landscape. Five field days held between the pine silvopasture sites at Americus GA and Chipley FL sites attracted a total of 275 participants. In May 2007 45 does and kids began foraging in the 3.89 hectare wooded experimental site at the Fort Valley State Agricultural Technology Center (ATC). By August 8, 2007 the does were depending on hay for their total feed supply. By this time both paddocks were completely devoid of vegetation except for three plant species. All other plant species had been consumed and some debarking of sweet gum trees was in progress. The three species of plant refused by the goats were: Sickle pod (Senna obtusifolia), Horse nettle (Solanum carolinense), and Spleenwort fern (Aspleniaceae spp.) These same species were observed to be refused by the goats the previous year. Although formal observations have not been made on changes in vertical light penetration into the area, it was obvious by the end of the 2007 season that understory growth was in retreat and visibility beneath the “goat line” was more open than in the past. This change is expected to enhance the growth and sustainability of grass and legume species that are able to support goat grazing over the longer term. A field day planned for the Fort Valley site in 2008 will provide some measure of landowner acceptance to the use of goat (or sheep) in vegetation management.

Objectives/Performance Targets

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. Examine the feasibility of using small ruminants for more sustainable control of invasive broadleaf plant species as herbicide use is reduced within developing silvopasture systems.
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

Objectives 1 and 2
Americus GA Site
A summary of the first 3 years data from the developing silvopasture site (4-7 yr old) was presented at and published in the proceedings of the 10th North American Agroforestry Conference, Quebec City Canada June 10-13, 2007 and subsequently invited for publication in a special agroforestry issue of Agriculture, Ecosystems and Environment.
Summary of the 3-yr (2005-2007) project results and conclusions at the Americus site.
March to August 2005 precipitation was consistently higher than the 47-y average except in May, but was consistently lower than the 47-y average in September and October. Precipitation in 2006 was consistently lower than the 47-y average from January to June, except in May, and in September. Precipitation also remained below the 47-y average from January to May, July, and from September to November 2007. With few exceptions, monthly average minimum and maximum temperature mostly remained similar for all three years (2005-2007).
Forage Productivity and Quality
There was a successful stand of clover in May 2005 and although the 2005 stand was managed to reseed, the May 2006 stand was sparse to non-existent in most plots. Overall, total forage shoot dry matter (SDM) production was not different between N sources. When analyzed over sampling dates, higher (P < 0.01) SDM was found for the legume- (3.8 ± 0.28 t ha-1) versus the fertilizer-N treatment (2.7 ± 0.40 t ha-1) in May 2005; this difference was observed for both pasture types. Crimson clover SDM was higher in legume- versus fertilizer-N plots in May 2005 and April 2007; conversely, SDM of other legumes was lower in legume- versus fertilizer-N for both of these sampling dates. Root dry matter was not different between N sources at either sampling date. Forage N concentration was not different between N sources, overall. However, when analyzed over sampling dates, higher N concentration was found in forage from legume- versus fertilizer-N treatment plots in May 2005 and April 2007. Conversely, in July 2007, forage-N concentration was lower for the legume- versus the fertilizer-N treatment. Forage ADF concentration was not different between N sources. No pasture-type effect was found on either total forage shoot or root dry matter production. However, SDM of crimson clover and total legumes were consistently less in silvo- versus open-pasture although the differences observed were not statistically significant. Lower N concentration was found in forage sampled from silvo- versus open-pasture in May and August 2006, and July and September 2007. Conversely, ADF concentration was higher in forage sampled from silvo- versus open-pasture in June and August 2006, and July and September 2007. There was no alley-position effect on SDM production in 2005; however, differences were found among alley positions in May 2006, and April, July, and September 2007. Crimson clover and total legume SDM were lower in 1.0- versus 3.5- or 6.1-m alley position in May 2005 and April 2007; conversely, SDM of legumes other than crimson clover was higher at the 1.0- versus 3.5- or 6.1-m alley position in April 2007. Pine straw biomass was higher at the 1.0- versus 3.5- or 6.1-m alley position for all sampling dates in 2006 and 2007. Root biomass was not different among alley positions for any sampling date. Forage N concentration was higher (P < 0.05) when sampled from 6.1-m (13.2 ± 0.55 g kg-1) versus 1.0-m position (11.8 ± 0.38 g kg-1) in July 2005. Forage N concentration was also different among alley positions in August 2006, and July and September 2007 (Table 3). Likewise, ADF concentration was higher in forage sampled from the 1.0- versus 3.5- or 6.1-m alley position in July and September 2007.
Soil Quality Indicators
Overall differences in water stable aggregates (WSA) were not detected between N sources. However, when analyzed over sampling dates, higher (P < 0.01) WSA concentrations were found in soils sampled from legume- (635 ± 22.9 g kg-1) versus fertilizer-N (555 ± 30.6 g kg-1) treatment plots in May 2006; this difference was observed for both pasture types. Density of fungal hyphae (DFH) was not different between N sources, overall. However, in August 2005, DFH was higher (P < 0.05) for the legume- (90 ± 3.6, m g-1) versus fertilizer-N (80 ± 3.4, m g-1) treatment; this response was observed only for open-pasture (100 ± 5.4, m g-1 vs. 79 ± 6.0 m g-1) when data from each pasture type were analyzed separately. Soil penetration resistance (PR) was not different between the N-source treatments in June 2005. However, in October 2007, PR was lower (P < 0.05) for legume- versus fertilizer-N treatment at 10-15- and 15-20-cm depths. Soil moisture was similar for both N treatments in June 2005 (legume-N: 9.7%, fertilizer-N: 10.0%) and October 2007 (legume-N: 10.8%, fertilizer-N: 11.1%). Lower (P < 0.01) concentrations of WSA were found in soils from silvo- (617 ± 8.3 g kg-1) versus open-pasture (650 ± 3.3 g kg-1) averaged over all dates, while DFH was higher (P < 0.05) in silvo- (58 ± 3.8 m g-1) versus open-pasture (46 ± 3.9 m g-1) in August 2006 only. June 2005 soil PR was lower in silvo- versus open-pasture at the 10-15-cm and 15-20-cm depths, and at the 15-20-cm depth in October 2007. However, the soil moisture was not significantly different between the pasture types at any date. Concentrations of WSA were similar at all sampling dates irrespective of alley position relative to the tree base. However, DHF was higher in soils from the 6.1- (87 ± 4.4 m g-1) versus the 1.0-m alley position (75 ± 3.0 m g-1) in August 2005. June 2005 soil PR was higher at 6.1- versus 1.0-m alley position for all depths; but only for depths greater than 0-5 cm in October 2007.
Conclusions
This research indicates that forage productivity and quality could be enhanced, and N fertilizer additions could be replaced by introducing and maintaining legumes into a pine-bahiagrass silvopasture system in the Southeastern US. Results also support the beneficial effect of legumes on soil quality. Pasture type was a major source of variation for water stable aggregates and penetration resistance of the soil studied. Moreover, alley position relative to trees in silvopasture caused differences in forage productivity and quality as well as soil penetration resistance. The effect of sampling date on all the variables measured was most likely the result of seasonal variation in climatic conditions and plant species present.
Protected Culture Studies – Auburn University
The objectives of this research were: 1) to determine the response of water stable aggregates (WSA) and density of fungal hyphae (DFH) in soil at the same pH supporting the growth of various forage species; 2) to determine the response of water stable aggregates and density of fungal hyphae associated with each forage species grown at two soil pH levels. Eleven cool-season (monoculture or legume-grass mixtures) and nine warm-season forage species (monoculture) were evaluated in three 12-week protected culture experiments during Fall 2005 (pH 5.0), and Summer (pH 5.0 vs. 6.9) and Fall 2006 (pH 4.8 vs. 6.5). Levels of WSA in soil that supported subterranean clover (Trifolium subterraneum) growth were greater than or equal to levels found in soil that supported other cool-season legumes, grasses, or mixtures studied. A similar relationship was found between Illinois bundleflower (Dismanthus illinoensis) and other warm-season forage species studied. DFH measured in soils that supported the growth of warm-season grass species was greater than levels measured in soils that supported warm-season legumes. Soil WSA and DFH levels were higher at low pH than high pH for several cool- and warm-season forage species. Field studies are needed to understand how these relationships are expressed in more variable environments over longer time frames.
Landscape Use and Activity of Cattle – Owen Farm, Chipley FL
Diurnal observations of cattle landscape use and activities were made March 26, June 29 and September 17 at the George Owen Farm, Chipley FL. Position and activities (grazing, lying, loafing) for six cows stocked in each 4-ha paddock (open or silvopasture) were observed and recorded at 15-minute intervals from dawn to dusk. Selection of landscape position was more even and grazing time longer for all diurnal periods for cows grazing silvopasture versus open pasture.

Objectives 3 and 4 – Fort Valley State University Site
On May 7, 2007 a total of 45 does and kids were moved to the 3.89 hectare wooded experimental site at the Fort Valley State Agricultural Technology Center (ATC). The experiment paddocks were the same as those used in the previous year and were selected to provide similar levels of ultraviolet rays and vertical open space. Water was provided ad libitum in each paddock as was supplemental trace-mineral salt. Animals were observed at least twice per day. Occasional breaks were made through the electric fence by individual animals when vegetation became scarce, but those became controlled after adjustments were made.
The goats were randomly allocated to one of two stocking…”light” or “heavy”. Initially the light stocking rate included 15 Spanish does averaging 48.9 kg and 22 nursing straightbred kids weighing an average of 15.46 kg. The heavy rate included Spanish 30 does averaging 42.5 kg and 47 nursing straightbred kids averaging 14.17 kg. The light stocking rate plot (1.3ha) initially supported a total 1081.82 kg or the equivalent of 832.17 kilograms per hectare. By comparison the heaving stocking rate plot (1.3ha) initially supported 1992.63 kg or the equivalent of 1532.79 kilograms per hectare.
On Day-18 the animals were removed from the study area because of dry conditions and a visual assessment verifying that adequate forage was longer available for maintaining body weight. The kids were subsequently weaned and removed from the study area. The does were moved to other grazing areas at the ATC awaiting the return of an adequate supply of vegetation in the experimental area.
Fecal samples were taken twice per week. Half of each sample was oven dried and half was placed in a test tube with water and refrigerated until shipped to the Auburn University laboratory. The chilled wet samples and the oven dried samples were shipped weekly in cold pack boxes by overnight express. Samples were processed at Auburn to determine plant cell contents and identify plant species composition. Plant species composition was a verification of plant availability and preference over the growing season.
On June 29, 2007 the does were returned to the grazing area to resume grazing. Animal observations and collection of fecal matter was continued as per the initial protocol. Without the kids the stocking density of the does was 564.55kg/hectare for the low stocking rate and 980.11 kg/hectare for the high stocking rate. Continued dry weather forced the feeding of supplemental Bermuda grass hay beginning on July 28, 2007. The hay was provided at the rate of about 20.4 kg to the heavy stocking group and 6.8 kg to the light stocking rate on an every other day basis. Small square bales were used and the sections were placed around each paddock so each animal had an opportunity to become filled without undue disturbance by more aggressive does. By August 8, 2007 the does were depending on hay for their total feed supply. By this time both paddocks were completely devoid of vegetation except for three plant species. All other plant species had been consumed and some debarking of sweet gum trees was in progress. The three species of plant refused by the goats were: Sickle pod (Senna obtusifolia), Horse nettle (Solanum carolinense), and Spleenwort fern (Aspleniaceae spp.) These same species were observed to be refused by the goats the previous year.
Although formal observations have not been made on changes in vertical light penetration into the area, it was obvious by the end of the 2007 season that understory growth was in retreat and visibility beneath the “goat line” was more open than in the past. This change is expected to enhance the growth and sustainability of grass and legume species that are able to support goat grazing over the longer term. Final species composition data to be collected in 2008 will verify or nullify that presumption.
It is too early in the study to begin compiling feasibility data and landowner acceptance of the practices. At the end when all experiment data have been reviewed, then the economic components will be added. A field day planned for 2008 will provide some measure of landowner acceptance to the use of goat (or sheep) in vegetation management.

Impacts and Contributions/Outcomes

Field Days 2007-2008
Owen’s Farm Chipley Florida (Florida Forest Stewardship Program, IFAS Extension, Auburn Unviersity) April 10, 2007
40 participants
Survey responses from: 10 landowners, 1 county forester, 5 natural resources professionals with other organizations; 1 county extension agent/director; 4 other.
According to survey responses from 21 participants: Respondents owned or operated 1,051,947 total acres of land; all respondents reported learning something new on the tour; 15 respondents planned to change an aspect of their forest management or planning. Field day resulted in press exposure for the project through 2 publications by Pam Golden in the June 2007 issue of a Southern Farmer : 1. A front-page article from an interview with Mr. George Owen (silvopasture producer) titled Pines plus cattle pay; page 4 article from an interview with Andy Andreasen (Washington Co FL Extension Specialist)titled Grazing grows profit in pines.

Jimmy Carter Plant Materials Center, Americus GA
February 2007 Burn demonstration in native grasses and silvopasture tour, 45 participants
November 2007 Wildlife management practices for planted pines (NRCS CP36 Program) and silvopasture tour, 45 participants
February 2008 Burn demonstration for native grass management and silvopasture tour , 30 participants
March 2008 Wildlife management practices for planted pines (NRCS CP36 Program) and silvopasture tour, 115 participants

Publications (April 2007-April 2008)
Research
Karki, U., M.S. Goodman, and S.E. Sladden. 2007. N source influences on forage and soil in southern-pine silvopasture versus open-pasture. In A. Oliver and S. Campeau, eds. When Trees and Crops Get Together. Proceedings of the 10th North American Agroforestry Conference, Quebec City, Canada, June 10-13, 2007.
Karki, U., M.S. Goodman, and S.E. Sladden. 200_. N source influences forage and soil in developing southern-pine silvopasture. Agriculture, Ecosystems and Environment (in review).
Producer-oriented
Andreasen, A, C. Demers, M. Goodman, G.C. Owens. 2007. Forest Stewardship Silvopasture Tour Participant Bulletin, 27 pp.
Golden, P. 2007. Pines plus cattle pay. Southern Farmer 6(6):1.
Golden, P. 2007. Grazing grows profit in pines. Southern Farmer 6(6):4.
Project featured in an article in the Summer-Fall 2007 Issue of Inside Agroforestry published by the USDSA-National Agroforestry Center: Ruark, G., M. Schoeneberger, R. Straight, B. Wight, K. Stuhr and R. D. 2007. A taste of silvopasture research In Inside Agroforestry 16(3):6-7 (http://www.unl.edu/nac/insideagroforestry.htm)
Data Analysis Complete ; Publications in preparation
Karki, U. and M.S. Goodman. 200_. Forage species and pH influence soil quality. Plant and Soil (Manuscript in preparation for submission April 2008).
Karki, U. and M.S. Goodman. 200_. Cover composition and species diversity of a coastal plain pasture during conversion to silvopasture. Journal of Rangeland Ecology and Management (Manuscript in preparation for submission June 2008).
Goodman, M.S., J.W. Prevatt, and U.Karki. 200_. Environmental and economic advantages of legume presence in southern-pine silvopasture systems. Agroforestry Technical Note, USDA National Agroforestry Center (Manuscript in preparation for submission .
Karki, U. and M.S. Goodman. 200_. Landscape use by cattle in silvopasture versus open pasture. Journal of Rangeland Ecology and Management (Manuscript in preparation for submission August 2008).

Presentations (April 2007-April 2008)
2008 Silvopasture Tour, George Owens Farm, Chipley,Washington Co, FL, April 10
2 presentations: Silvopasture vs Open-Pasture Weather in Mature Silvopasture (field, oral presentation by M.S. Goodman) and Update on SARE Project (lunch, oral presentation by M.S. Goodman)N source influences on forage and soil in southern-pine silvopasture versus open-pasture. 10th North American Agroforestry Conference, Quebec City, Canada, June 10-13, 2007 (oral presentation by U. Karki).
Karki, U., M.S. Goodman, and S.E. Sladden. 2008. Forage productivity and quality dynamics in southern- pine silvopasture versus open-pasture. In Abstracts, Annual Meeting Society for Range Management, Lexington, KY, Jan 26-31, 2008 (oral presentation by U. Karki).
Karki, U. 2008. N source and tree interactions influence forage productivity and quality in developing silvopasture. Graduate Research Forum, Auburn University, March 11, 2008. (poster presentation by U. Karki).

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