Effect of Hole Size, Organic Amendments, and Surface Mulches on Tree Establishment in Southwestern Soils
Southern live oak (Quercus virginiana), and South American mesquite (Prosopis alba) were planted in a shallow soil (≈15 cm deep) underlain by indurated calcium carbonate in Tucson, Ariz. Oaks were planted in three hole sizes, with backfill amended or unamended with undigested wood material and with or without 9 cm of an organic surface mulch. The surface mulch was a blend of undigested wood material and yard waste compost. Initial oak trunk diameters were ≈2 cm. Mesquites were planted according to these treatments: 1) a hole 150 cm square with amended backfill, 2) a hole twice as wide and 30 cm deeper than the root ball with amended backfill, and 3) a hole five times as wide and no deeper than the root ball with unamended backfill. Initial mesquite trunk diameters were ≈4 cm. Sixteen (oaks) and 28 (mesquites) months after planting soil was removed from the planting holes by a sewage vacuum truck. We will report the effect of treatments on trunk and canopy growth, and root growth from the side and beneath the original root ball.