Individual and Combined Use of Sawdust and Weed Mat Mulch in a New Planting of Northern Highbush Blueberry I. Impacts on Plant Growth and Soil and Canopy Temperature

Abstract

A 2-year trial was established in Oct. 2016 in western Oregon to evaluate the effects of various in-row mulch treatments on the establishment of northern highbush blueberry (Vaccinium corymbosum L. ‘Duke’). The treatments included douglas fir [Pseudotsuga menziesii (Mirb.) Franco] sawdust, black weed mat (woven polypropylene groundcover), green weed mat, and sawdust covered with black or green weed mat. Soil temperature was unaffected by the color of the weed mat, but it was often higher during the day in beds with weed mat mulch than in those with sawdust alone or sawdust covered with weed mat. Black or green weed mat also resulted in higher canopy temperatures, particularly when sawdust was underneath the weed mat. Plant growth was mainly unaffected by the color of the weed mat, and the maximum depth of the root system was similar among the mulch treatments. However, plants grown with sawdust mulch, with or without weed mat, had a greater canopy width and volume in year 2, a wider root system in both years, and more dry weight (DW) in the crown in year 1 and in the whips in year 2 than those with weed mat alone. Furthermore, plants with weed mat over sawdust were taller in year 1 and had greater canopy cover and more DW in new wood in year 2 than those with sawdust alone, and they had a larger canopy, more root development, and greater DW in the crown, new and old wood, fruit, and pruning wood in one or both years than those with weed mat alone. Over the course of the 2 years of the study, the net gain in total plant DW was lowest when the plants were grown with black weed mat and highest when they were grown with black weed mat over sawdust. Although it was more expensive initially, the use of weed mat over sawdust resulted in more plant growth than weed mat alone due to the insulating properties of the sawdust, and it was more effective for weed control than using sawdust alone.