1. Photosynthically Active Radiation Use Efficiency of Dactylis glomerata in a Hardwood Silvopasture Charlie Feldhake Dave Belesky

2. Photosynthically Active Radiation Use Efficiency of Dactylis glomerata in a Hardwood Silvograss-sward Charlie Feldhake Dave Belesky

3. USDA-ARS Appalachian Farming Systems Research Center Beaver, West Virginia

4. Appalachia is 23% larger than the state of California

6. Question 1: How efficiently does orchardgrass utilize PAR at different PAR levels under deciduous trees?

7. Question 2: Do juvenile plants function differently than vernalized (mature) plants?

10. (0) Open Site (Eo) 2 m within forest edge (Ew) 7 m within forest edge (W) 30 m within forest

11. Grasses were grown in 15 cm dia. pots which were placed in the ground after bottoms were removed One set placed in May 2001 Another in August 2001 for harvesting in 2002 3 Harvested at 20 cm height, others clipped to 5 cm

16. Table 1. Summer solstice (7-week average) actual and relative PAR. Measurement Site OEoEwWMax PAR (Mol m -2 d -1 ) 200139.718.79.74.9 59.3 200226.810.76.93.7 59.3 % of Open (100-Shade) 2001100472412 2002100402614 % of Max 20016732168 20024518126

20. PAR Use Efficiency is equal to total PAR summed from the previous harvest divided by dry leaf mass.

22. PAR Use Efficiency Eo/O Ew/W W/O 2001 1.4 3.4 3.0 2002 1.2 1.7 2.6

23. Given one of the most important objectives of agriculture is to harvest solar radiation for human use, then C3 grass open pasture in a temperate, humid climate is not a very efficient way to do it.

24. But: These Grass Roots Were Not Competing With Tree Roots. What Happens In The Real World?

27. Leaf Growth Decreased With Daily PAR But Less Rapidly. There Was Less Than A 2-Fold Increase In PAR Use Efficiency.

30. Leaf Growth Did Not Decrease With Daily PAR. There Was A 5- Fold Increase In PAR Use Efficiency.

31. The Duration Of Daily PAR Is Important In Addition To The Amount Of Daily PAR.

32. Forages Under Deciduous Trees Also Receive A Spring And Autumn “Spike” In PAR That Does Not Happen Under Conifers

33. If you can utilize much of the solar radiation by trees midday through early afternoon and during peak summer intensities you can substantially increase overall system solar radiation harvesting efficiency.

34. Star PAR Extra-Solar PAR contributes about 5 mg ha -1 yr -1 to corn grain yield.