Effect of Loblolly Pine Root Pruning on Alley Cropped Herbage and Tree Growth.

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.  We compared tillage effects on 9- to 11-year-old loblolly pine (Pinus taeda) growth and yields of annual ryegrass (Lolium multiflorum) and pearl millet (Pennisetum glaucum) in an alley cropping practice in Arkansas.  Alley crops were rotationally-grown in a 9.7-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 among subplots compared to the other tillage treatments, but only modest improvements in crop yield.  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 could not be justified for annual herbage or wood fiber in this marginally productive loblolly pine alley cropping practice.