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

<jats:p>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 (<jats:italic>Vaccinium corymbosum</jats:italic> L. ‘Duke’). The treatments included douglas fir [<jats:italic>Pseudotsuga menziesii</jats:italic> (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.</jats:p>

Individual and Combined Use of Sawdust and Weed Mat Mulch in a New Planting of Northern Highbush Blueberry. II. Nutrient Uptake and Allocation

“…We reported earlier that weed mat color (black and green) had little effect on plant growth, but blueberry plants established with weed mat over sawdust mulch had a higher net gain in total plant DW over 2 years of establishment than those grown with black weed mat alone (Strik et al, 2020).…”

“…Plants that were destructively harvested were pruned similarly to the rest of the treatment plants, but pruning wood was kept separate (as discussed later in the article). Further details on site preparation and cultural management are provided by Strik et al (2020).…”

“…Nutrient content, allocation, and uptake. The nutrient content of each plant part was calculated from nutrient concentration (analysis results) and the biomass of the corresponding plant part (results presented by Strik et al, 2020). Total nutrient gains (plant content in new wood, old wood, whips, crown, and roots relative to the prior season) and losses (through senesced leaves and pruning wood in 2017 and 2018 and fruit in 2018) were calculated each year and used to determine nutrient uptake from planting to the end of the second growing season.…”

“…Higher soil NO 3 -N and NH 4 -N were found in blueberry and blackberry under a black weed mat mulch compared with sawdust or bare soil, respectively (Dixon et al, 2016;Larco et al, 2013;Strik et al, 2019), likely a result of higher soil temperatures under the weed mat increasing mineralization of organic matter or nitrification (Larco, 2010). Adding a layer of sawdust under the weed mat reduced soil temperature compared with weed mat alone (Strik et al, 2020), perhaps reducing nitrification as reflected by lower levels of soil NO 3 -N. However, soil NO 3 -N was higher under sawdust mulch than weed mat over sawdust (Table 1), despite the former having the lowest soil temperature (Strik et al, 2020). Soil levels of NO 3 -N and NH 4 -N in the autumn are likely related to fertilizer remaining after plant uptake and the impact of soil temperature on nitrification.…”

“…Weed mat is becoming more common because it is more economical for weed control than sawdust, and it can have a positive effect on yield in blueberry (Strik et al, 2017a;Strik and Vance, 2017). Weed mat captures more longwave radiation and results in warmer soil temperatures than organic mulches, such as sawdust or wood chips (Cox, 2009;Larco, 2010;Strik et al, 2017aStrik et al, , 2020. Weed mat may also change soil nutrient levels and soil properties, such as organic matter and pH, thus affecting nutrient availability in blueberry (Strik et al, 2019).…”