Initial growth of irrigated hybrid poplar decreased by ground covers

Abstract

Four ground covers were compared with bare soil for their effects on the growth of irrigated poplar trees from 1997 through 1999 at the Malheur Experiment Station near Ontario, OR. Stem cuttings of hybrid poplar (Populus deltoides × P. nigra, clone 'OP-367') were planted in April 1997 at a 14 × 14-ft spacing. Ground cover treatments consisted of(1) bare soil maintained with a preplant herbicide and cultivations, (2) mowed weeds, (3) wheat (Triticum aestivum) between tree rows, (4) alfalfa (Medicago sativa) between tree rows, and (5) squash (Cucurbita maxima) between tree rows. The field was irrigated uniformly using micro sprinklers along the tree rows. Wood volume at the end of September in 1997 and 1998 was significantly greater for the bare soil than any ground cover. By the end of September 1998, wood volume in bare soil plots was more than 100% greater than in mowed weed plots, and almost 50% greater than in squash plots. During the third growing season, the incremental growth of wood volume was similar among the bare soil treatment, mowed weeds, and the plots that had previously been planted to squash but remained bare in the third year due to closure of the tree canopy. Without consideration of the economic value of cover crops, results suggest that, in eastern Oregon, poplar wood volume during the first three years is the greatest when the ground is kept bare. West. J. Appl. For.