Author
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Feldhake, Charles |
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Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/20/2009 Publication Date: 5/27/2009 Citation: Feldhake, C.M. 2009. Forage Evapotranspiration and Photosynthetically Active Radiation Interception in Proximity to Deciduous Trees. Agricultural Water Management. 96:1170-1174. Interpretive Summary: There is a lot that is not understood about the impact of trees in silvopasture systems on understory forage production. Understanding how microclimate modification by trees impacts forage water requirements is an important knowledge component needed to design productive systems. Small bucket weighing lysimeters were used to measure actual water use by forages in a wide array of positions relative to trees. Water use did not decrease in proportion to decreases in solar radiation in response to tree shade. On a percentage basis, wind and low relative humidity had greater impact on shaded forage water use than on forages in full sun. This work will be useful to scientists in understanding the potential productivity of different silvopasture configurations. It will be useful for helping forage producers predict forage yields and couple that production to seasonal animal requirements. It will help increase and diversify small farm income using forages and trees on the same land units. Technical Abstract: Practically all of the extensive body of research on evapotranspiration (ET) in agricultural systems has been done for open fields. There is a lack of good information on how the microclimate variability within silvopasture systems affects water requirements of forages. Small 26 cm diameter, 23 cm deep lysimeters planted with either orchardgrass (Dactylis glomerata L.) or tall fescue (Lolium arundinaceusm (Schreb.) S.J. Darbyshire) were placed in the ground along the north and south edge of two 15 m wide by 50 m deep notches cleared into a mature second growth hardwood forest. One notch opened to pasture on the east receiving more early day solar radiation and one to pasture on the west receiving more wind and late day solar radiation. There was no significant difference in ET between orchardgrass and tall fescue. North edges, receiving more direct beam radiation, had significantly higher ET (39%) than south edges which received a higher percentage of diffuse radiation. The west notch had significantly higher ET (11%) than the east notch. At the sunniest sites, advection provided 20% of the energy used for ET while at the shadiest sites it provided more than half (56%) with the rest provided by incident solar radiation. Dates where photosynthetically active radiation (PAR) was restricted by clouds resulted in decreased ET relative to PAR compared to more sunny days. However, sites where PAR was restricted by tree shade had higher ET relative to Par than more open sites. These results indicate tree modification of microclimate does not decrease forage ET to the extent that PAR is decreased. |
