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

Open pasture produced more forage (17,200 kg/ha) than each of the two silvopastoral systems studied. Similarly, the double tree-row silvopasture outperformed scattered tree silvopasture by 2,000 kg/ha producing 13,650 kg/ha dry matter yield. Adding ryegrass and crimson clover to forage plots significantly increased annual forage production for each added species. However, adding a second clover species did not produce further yield increases. Seasonal weighed forage quality indices were not affected by either tree canopy treatments, nor by forage species/varieties tested. Average stem volume was greater, but trees had larger crowns in the silvopastures than conventionally 5th row thinned pine plantation.

Objectives/Performance Targets

• Evaluate effects of tree canopy configuration and forage species and variety composition on monthly, seasonal and yearly forage yield and quality obtained in two silvopastoral systems with those obtained for the same forage species and variety combinations in open pasture.

  Compare tree growth and tree crown characteristics in two silvopastoral systems with those obtained for conventionally 5th row thinned pine plantation.

Accomplishments/Milestones

Forage Yields
As expected we found that open pasture produced more total herbage mass (17,200 kg/ha) than any of the two silvopastoral systems studied. Similarly, double tree-row silvopasture outperformed the scattered tree silvopasture by about 2,000 kg/ha dry matter yield annually. The total forage production in the double tree-row silvopasture reached 13,650 kg/ha in 2005. Also, on a seasonal basis, open pasture produced more winter and summer forage mass than any of the two silvopastoral systems. During the cool growing season, the double tree-row silvopasture produced 6,800 kg/ha of forage mass and outperformed the scattered tree silvopasture which yielded 5,200 kg/ha, but during the warm season, the differences in forage production between the two silvopastoral systems (9,400 vs. 8,700 kg/ha, respectively) were statistically insignificant.

Forage species combination had a significant effect on the amount of herbage mass produced. In winter 2005 forage production reached 7,100 kg/ha in ryegrass plus crimson clover plus red clover species combination plots, and was only insignificantly lower when crimson clover was the only leguminous species present in the system. During summer, bahiagrass only plots (no winter forages planted), produced more herbage mass than plots containing ryegrass and one or two clovers in the cool seasons. Plots containing clovers in winter did not differ from each other in bahiagrass production, and yielded more bahiagrass than plots containing ryegrass as the only cool season forage. However, total forage production was the lowest in bahiagrass only plots, higher in plots containing ryegrass, and the highest in plots containing clovers. There were no significant differences in total yearly forage dry mass produced due to the number of clover species planted, i.e., plots with crimson clover only, and plots containing crimson clover plus red clover yielded similar amounts of total forage dry mass. Total forage production peaked at 16,100 kg/ha in 2005 for plots containing all four forage species.

Monthly harvests from February until May 2005, revealed that winter forage production was increasing gradually in all production systems toward the end of the cool growing season. The open pasture outperformed the silvopastoral systems every month, except for May 2005, when the double tree-row silvopasture produced almost as much forage (2,600 kg/ha) as the open pasture (2,800 kg/ha), with the difference between the two being statistically insignificant. The differences in monthly winter forage production between the two silvopastoral systems were all insignificant for every harvest, except for May 2005 when the scattered tree silvopasture produced less forage (2010 kg/ha) than the double tree-row silvopasture (2600 kg/ha). Also winter forage species composition did not have a significant effect on forage yield produced until May 2005 when plots containing one (2500 kg/ha) or both (2,700 kg/ha) clover species outperformed the plots with ryegrass planted as the only cool season forage.

Monthly bahiagrass forage production during warm growing seasons of 2005 was consistently higher in the open pasture than the silvopastoral systems. Double tree-row silvopasture outperformed scattered tree silvopasture in the last sampling of October 2005. Plots where only bahiagrass was planted produced more dry matter yield than plots with clovers during the first harvest of the warm season, and more dry matter yield than ryegrass containing plots during the first two and then the last harvests of 2005 warm growing season. These results suggest that presence of clovers during cool growing season interfered with bahiagrass production during warm growing seasons less than presence of ryegrass.

Forage Quality
For winter forages, monthly in vitro organic matter digestibility (IVOMD) was the highest at the beginning of the cool growing season. The highest IVOMD values were recorded for ryegrass plots in February through April harvests, but for May harvest, the plots containing one or two clover species had significantly higher IVOMD values than those containing ryegrass only. Average weighed IVOMD across all treatments and sampling times was 80.0%.

Crude protein content (CP) for winter forages grown in the open pasture was higher than in the silvopastures in February through March 2005. Later in the 2005 cool growing season for April and May samplings, forages in the double tree-row silvopasture had the highest CP content among the three systems under study. However the late season CP values (16.2%) were only about half of the peak values (29.2%) reached in February 2005. The CP values where higher in clover than ryegrass containing plots only for May 2005 sampling. Average weighed CP across all treatments and sampling times was 22.1%.

Percent phosphorus (P) in winter forages did not differ significantly among the tree canopy or forage treatments. The highest value of 0.47 was recorded for open pasture in April 2005. Across all treatments and sampling times average weighed P was 0.38%.

Summer forage percent in vitro organic matter digestibility (IVOMD) was higher in open pasture than in one or both silvopastoral systems in June and October 2005. The same was true for plots containing all four forage species for June and October 2005 samplings. Summer (bahiagrass) forage IVOMD was only about 62% of that for winter forages. Across all treatments and sampling times average weighed summer forage IVOMD was 49.3%.

Crude protein (CP) content of summer forages varied little among the thinning treatments in 2005. Addition of two clovers to forage mixes in winter increased CP in summer forage (bahiagrass) significantly from June to October 2005. Across all treatments and sampling times average weighed summer forage CP was 11.5% in 2005. The summer CP contents constituted on average 52% of CP measured in winter forages.

Phosphorus (P) content in summer forage was higher in open pasture than other tree canopy treatments in June 2005. Increasing the number of winter forage species planted on a plot tended to increase summer forage P content. Across all treatments and sampling times average weighed summer forage P was 0.26% in 2005. This value represents 68% of the winter forage P contents in 2005.

Tree and Stand Growth
Overall tree and stand growth characteristics measured in the two silvopastures and the conventionally 5th row thinned pine plantation conformed to the expectations. Average tree height in the conventionally 5th row thinned pine plantation was larger than in the silvopastures. The opposite was true with regard to DBH, i.e., an average tree in the conventionally 5th row thinned pine plantation was thinner than those in the silvopastures throughout the study. Similarly, as expected, average height to the first live branch was less in the silvopastures than in the conventionally 5th row thinned pine plantation in the same time period. Consequently, average crown length was the largest in the double tree-row silvopasture, intermediate in the scattered tree silvopasture and the smallest in the conventionally 5th row thinned pine plantation for the duration of the study. Also average crown widths were larger in the silvopastures than in the conventionally 5th row thinned pine plantation at the end of the study in 2005. During the time of the experiment, both silvopastures did not differ with respect to average tree height, DBH, height to first live branch, and average crown widths. As a consequence of the tree dimensions, an average tree volume was higher in the silvopastures (and not different between the two) than in the conventionally 5th row thinned pine plantation. However, wood volume per unit of land area was also higher in the silvopastures than conventionally 5th row thinned pine plantation. This was likely an effect of higher tree mortality in the conventionally 5th row thinned pine plantation than in the silvopastures after a prescribed fire applied to all systems in April 2003. During the experiment between 2003 and 2005 the overall, across thinning treatments average tree growth variables changed as follows: height from 17.95 m to 18.80 m, DBH from 23.3 cm to 26.4 cm, height to first live branch from 9.67 m to 10.39 m, crown length from 8.27 m to 8.41 m, crown width from 3.52 m to 4.19 m, tree volume from 0.26 to 0.35 cubic meter, and wood volume per unit land area from 56.98 to 76.60 cubic meter per hectare.

Impacts and Contributions/Outcomes

To date, the project had limited impact on Florida landowners and county extension agents who are still learning about the project results and their applicability to farm operations and/or extension clientele. It is expected that the project will have greater impact in the future when cattle is incorporated into the silvopastoral systems created in the course of this project.

Collaborators: