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Title: Photosynthetically active radiation use efficiency of Dactylis glomerata and Schedonorus phoenix along a hardwood tree-induced light gradient

item Feldhake, Charles
item Belesky, David

Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2008
Publication Date: 1/30/2009
Citation: Feldhake, C.M., Belesky, D.P. 2009. Photosynthetically active radiation use efficiency of Dactylis glomerata and Schedonorus phoenix along a hardwood tree-induced light gradient. Agroforestry Systems. 74:189-196.

Interpretive Summary: Appropriate silvopasture systems for the Appalachian Region are difficult to design because of light conditions that vary spatially due to trees and topography, seasonally, and yearly as long term weather patterns change. Better knowledge is therefore needed on how efficiently forages convert solar radiation into herbage for feeding grazing livestock under different light conditions. Forage yield was analyzed in relation to light along a deciduous forest edge that imposed a light gradient on container-grown orchardgrass and tall fescue, two common forage grasses in Appalachia. An extensive array of solar radiation sensing equipment was used to quantify the light gradient throughout three growing seasons. The results show that while there is an increase in yield at higher solar radiation-receiving sites, there was an exponential increase in the efficiency with which solar radiation was converted to leaf herbage as total solar radiation interception decreased. This work is useful because it helps us predict how much solar radiation can be allocated to trees for conversion to other products and still grow livestock-sustaining forage. Silvopastures will benefit the economy in Appalachia by helping farmers increase and diversify income streams and add economic resilience to rural communities. By diversifying products grown it will also facilitate development of small, local value-added industries.

Technical Abstract: Optimal management strategies for conversion of hardwood forests in Appalachia to productive silvopastures are not available. The relationship between available understory photosynthetically active radiation (PAR) and forage productivity is not well understood for thinned mature hardwood forests. An experiment using container-grown plants was conducted under field conditions to determine how PAR levels influenced productivity and PAR-use-efficiency (PARUE) in Dactylis glomerata L. and Lolium arundinaceum Darbysh. Plants harvested during the summer were established in early spring, and for orchardgrass, also in the autumn to allow vernalization for harvesting the second year. Pots were clipped whenever the forage in a treatment reached a 20 cm height, leaving a 5 cm residue to simulate grazing. Plants established in the autumn had fewer but larger tillers. Due to cloudiness, the open field treatment received 67, 45 and 55% of maximum possible mid-summer PAR for 2001, 2002 and 2004 respectively. Total yield increased with daily PAR received, however, maximum PAR-use-efficiency was achieved at sites receiving less than 20% of maximum PAR due to tree shading. The differences in physiological and morphological response to PAR suggest that management needs to be flexible and vary between radiation zones to optimize production. Forage grass response to various PAR levels suggests a high degree of plasticity in terms of productivity and resource allocation even though the cultivars used were developed for high productivity in open field sites. Selecting or breeding forages for minimal nitrate accumulation and maximum total non-structural carbohydrate accumulation under shade may be key to increasing temperate silvopastoral productivity.