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

Authors: STRIK, BERNANDINE - Oregon State University; DAVIS, AMANDA - Oregon State University; Bryla, David; Orr, Scott

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2020
Publication Date: 8/1/2020
Citation: Strik, B.C., Davis, A.J., Bryla, D.R., Orr, S.T. 2020. 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. HortScience. 55(8):1280-1287. https://doi.org/10.21273/HORTSCI15122-20.
DOI: https://doi.org/10.21273/HORTSCI15122-20

Interpretive Summary: Many growers are using woven polypropylene ground cover, which is often referred to as “weed mat”, in commercial blueberry fields. Weed mat is very cost effective for weed control, but, unlike the previous industry standard of using sawdust mulch, it leads to a reduction in soil organic matter within a few years of planting. Blueberries prefer soils with high organic matter content, so finding a mulch system where this decline can be prevented would be of great benefit. ARS researcher in Corvallis, OR and collaborators from Oregon State University evaluated the potential of using a combination of sawdust and weed mat in a new planting of blueberries. Adding a layer of sawdust under the weed mat resulted in a larger root system by the end of the first year and larger plants by the end of the second year than weed mat alone. Basically, sawdust served as an insulator between the weed mat and soil, reducing soil temperature to a better range for blueberry. Weed mat, on the other hand, protected the sawdust layer from erosion by wind and rain and was more effective for weed control than sawdust alone. Additional measurements are underway to examine the effects of these mulches on plant nutrition and fruit production.

Technical Abstract: A 2-year trial was established in Oct. 2016 in western Oregon to evaluate the effects of various in-row mulch treatments on establishment of northern highbush blueberry (Vaccinium corymbosum L. ‘Duke’). The treatments included douglas fir [Pseudotsuga menziesii (Mirb.) Franco] sawdust, black weed mat (woven polypropylene ground cover), green weed mat, and sawdust covered with black or green weed mat. Soil temperature was unaffected by the color of the weed mat but was often higher during the day in beds with weed mat mulch than in those with sawdust or sawdust covered with weed mat. Black or green weed mat also resulted in higher canopy temperatures, particularly when there was sawdust underneath the weed mat. For the most part, plant growth was unaffected by the color of the weed mat, and the maximum depth of root system was similar among the mulch treatments. However, plants grown with sawdust mulch had 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 2 years of the study, net gain in total plant DW was lowest when the plants were grown with black weed mat mulch and highest when they were grown with black weed mat over sawdust. While 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 was more effective for weed control, and perhaps was less costly over time, than using sawdust alone.