Performance of Various Forage Combinations Under Thinned Pine Canopies in North Florida

Performance of Various Forage Combinations Under Thinned Pine Canopies in North Florida

Summary

Winter forage yield and digestibility were higher in the open pasture compared with the silvopastoral systems studied. These differences were attributed to shading by trees evidenced by differences in Photosynthetically Active Radiation (PAR) between the open pasture and the silvopastures. Due to a larger number of trees per unit of land area, more wood volume was produced in the conventionally 5th-row thinned loblolly pine plantation than in the silvopastoral systems.

Objectives/Performance Targets

Objective 1: Silvopasture establishment after tree stand thinning

Objective 2: Forage yield and quality in silvopasture compared to open pasture

Objective 3: Tree growth in silvopasture compared to pine plantation

Accomplishments/Milestones

Objective 1: Silvopasture establishment after tree stand thinning
Status: Accomplished (see Report for 2003)

Objective 2: Forage yield and quality in silvopasture compared with open pasture
Status: Field work accomplished, results for winter 2004 forages were analyzed and are presented below.
Procedures:
Yield and quality of the following forage combinations were tested under two pine canopy conditions in comparison with open pasture: (i) Argentine bahiagrass alone; (ii) Argentine bahiagrass plus Jumbo ryegrass; (iii) Argentine bahiagrass plus Jumbo ryegrass plus Dixie crimson clover; (iv) Argentine bahiagrass plus Jumbo ryegrass plus Dixie crimson clover plus Cherokee red clover. Winter forage harvest and evaluation were conducted between February and May 2004, while summer forage harvest and evaluation were between June and November 2004. Within the appropriate season, the forages were harvested every 4 weeks by clipping within exclusion cages. The following parameters were measured: (i) herbage dry mass; (ii) weed dry mass; (iii) nutritive value (crude protein and in vitro organic matter digestibility).

Results to date:
Total pasture dry matter (DM) yield for the 2004 winter season (6.75 Mg/ha) was higher compared with DM in silvopastoral systems. The silvopastoral system with trees arranged in double-row sets and forage alleys between the sets (referred to as “double-row” treatment) and the silvopasture with random tree placement (referred to as “heavy thinning” treatment) were not significantly different with respect to winter forage yield produced (4.37 Mg/ha and 3.97 Mg/ha, respectively). Forage species combination treatments had no effect on total forage DM for the winter season.
More ryegrass and clover DM was produced in the open pasture than in the double-row or heavy thinning treatments. The forage treatments containing clovers produced less ryegrass. Increasing the number of clover species from one to two resulted in significantly higher (30% difference) clover total DM. Neither the tree canopy conditions nor the forage treatments had significant effects on the weed total DM during the winter season.
Average forage In Vitro Organic Matter Digestibility (IVOMD) was lower in silvopastures compared with the open pasture where IVOMD averaged 65%. However, the IVOMD in the double-row (61%) and heavy thinning (62%) treatments were not significantly different from each other. Overseeding with clover(s) lowered IVOMD from 64% for ryegrass only treatments to 62% for ryegrass plus clover(s) forage combinations.
More Photosynthetically Active Radiation (PAR) was available to winter forages grown in the open pasture than in the silvopastoral systems, which on average received 87% of full sunlight. This was reflected in the higher total DM, ryegrass, and clover yields in the open pasture compared with the silvopastures. However, weed herbage DM was not significantly affected by PAR differences.

Objective 3: Tree growth in silvopasture compared with pine plantation
Status: Field work accomplished, 2004 tree measurements were analyzed and are presented below
Procedures:
Tree heights, diameters at breast height (DBH), and crown widths in two perpendicular directions were measured in January 2004 and again in January 2005. This data allows tree growth and crown characteristics comparisons between the silvopastures and conventionally 5th-row thinned pine plantations. In addition, tree foliage was sampled in February 2004 and February 2005. Tree foliage has been analyzed for N, P, K to determine the impact of silvopasture fertilization on tree nutrition, but these results are not available yet.

Results to date:
Thinning treatments had significant effects on tree growth parameters measured in January 2004. Average tree height was larger in the heavy and conventionally 5th-row thinned treatments than in the double-row treatments. Average tree diameter was the lowest in the conventionally 5th-row thinned treatments. However, overall more wood was produced in the conventionally 5th-row thinned (79 m3/ha) than silvopastoral treatments (53 m3/ha in heavy thinning treatment, and 63 m3/ha in double row treatment). The wood volume differences were due to the number of trees per unit land area and not differences in tree diameter or tree height among the treatments.
Tree crowns were affected by the thinning treatments as expected. Average crown widths were larger in the double-row and the heavy thinning than in the conventionally 5th-row thinned treatments. Tree crown lengths were the largest in the double-row, and the smallest in the conventionally 5th-row thinned treatments. Crown length differences were due to height to the first live branch and not tree height differences.

Impacts and Contributions/Outcomes

On 18 March 2004, the silvopasture experiment was presented to 10 Florida county extension agents and 4 Florida Division of Forestry foresters attending agroforestry in-service training at the UF/IFAS North Florida Research and Education Center near Quincy, FL. In addition, the preliminary results and techniques generated by this project were presented respectively, as a poster to all attendees, and an oral presentation to the participants of the pre-conference workshop on silvopasture, during the 1st World Agroforestry Congress in Orlando, FL, 27 June – 2 July 2004.

Publications to date:
Bambo, S., Nowak, J., Blount, A., Osiecka, A. and Myer, R. 2004. Loblolly pine growth and warm/cool season forage performance under thinned tree canopies in North Florida (abstract). Book of Abstracts, 1st World Congress of Agroforestry, Orlando, FL, 27 June – 2 July 2004.

Collaborators: