Effect of Loblolly Pine (Pinus taeda L.) Root Pruning on Alley Cropped Herbage Production and Tree Growth

Authors: Burner, David; Pote, Daniel; Belesky, David

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2008
Publication Date: 1/8/2009
Citation: Burner, D.M., Pote, D.H., Belesky, D.P. 2009. Effect of loblolly pine root pruning on alley cropped herbage production and tree growth. Agronomy Journal. 101(1):184-192.

Interpretive Summary: The co-production of agricultural crops and trees on the same land area (agroforestry) reduces yield of one or both crops because of competition for light and soil water. Pruning of tree branches and selective removal of trees (thinning) are standard approaches for increasing light reception by the understory crop, and some have suggested that pruning the tree roots could be similarly effective by increasing soil water availability to the crop. Indeed, producers have been able to obtain cost share incentives for pruning tree roots. Nevertheless, the actual effect of root pruning on trees and crops is poorly understood. The objective of this study was to determine if pruning the roots of loblolly pine trees, either with a standard ripping implement or trenching, could improve yields of two grass crops, annual ryegrass and pearl millet, without affecting tree growth. Crop yields were not consistently improved, and tree growth was reduced, when tree roots were pruned. Root pruning did not appear to be justified in this loblolly pine production system.

Technical Abstract: The competitive irradiance constraint of trees on the understory can be reduced by foliar pruning. Use of tillage to disrupt (prune) tree roots is an intensive practice which could improve herbage productivity at the crop-tree interface by reducing competition for water. Our objective was to compare tillage effects on growth of 9- to 11-year-old loblolly pine growth and yields of annual ryegrass and pearl millet in an alley cropping practice near Booneville, Arkansas. Alley crops were rotationally-grown in a 10-m wide alley (main plot) between bordering trees on one of three tillage treatments: control (surface tillage), rip followed by surface tillage, and trench plus root barrier followed by surface tillage. Topsoil water in May through September, herbage mass, and nutritive value were measured for each crop for 2 or 3 years in three subplots systematically arrayed (north, middle, and south) across the alley. Diameter and height of border trees were measured annually. Ripping and trenching significantly reduced loblolly pine dbh and height compared to the control. Trenching resulted in a more uniform distribution of topsoil water across the alley compared to the other tillage treatments. Ripping and trenching improved herbage yield one of two (annual ryegrass) or two of three (pearl millet) crops, and caused no consistent improvement in herbage nutritive value. The imposition of intensive tillage practices could not be justified for annual herbage or wood fiber in this marginally productive loblolly pine alley cropping system.