Individual and combined use of sawdust and weed mat mulch in a new planting of northern highbush blueberry. II. Nutrient uptake and allocation

Authors: STRIK, BERNADINE - Oregon State University; DAVIS, AMANDA - Oregon State University; Bryla, David

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2020
Publication Date: 10/1/2020
Citation: Strik, B.C., Davis, A.J., Bryla, D.R. 2020. Individual and combined use of sawdust and weed mat mulch in a new planting of northern highbush blueberry. II. Nutrient uptake and allocation. HortScience. 55(10):1614-1621. https://doi.org/10.21273/HORTSCI15271-20.
DOI: https://doi.org/10.21273/HORTSCI15271-20

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. An ARS researcher in Corvallis, OR and collaborators from Oregon State University examined the nutrient requirements during establishment in a new planting of blueberry with different types of soil mulches, including sawdust, weed mat, and weed mat over sawdust. Plants were only fertilized with nitrogen during the study because soil and leaf tests indicated that other nutrients in the field were sufficient for growing blueberries. The percentage of the total nitrogen in the plants derived from fertilizer was lowest with weed mat and highest with weed mat over sawdust. The gain in other nutrients was small and derived from soil or decomposing roots. It is clear that blueberry plants have a low requirement for other nutrients regardless of mulch type. Results from the study will help growers increase the efficiency of fertilizer use in blueberry.

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. For the most part, plant nutrient concentration and content were unaffected by the color of the weed mat. In both years, mulching with weed mat over sawdust reduced soil nitrate-N as compared to weed mat alone. The only other soil nutrient affected by mulch was K, which was highest with sawdust mulch and intermediate with black weed mat alone in year 2. There were inconsistent effects of mulch on leaf nutrient concentration during the study. In 2018, leaf N concentration was lowest with black weed mat over sawdust. There were few mulch effects on nutrient concentrations in senescent leaves in both years and in harvested fruit in year 2. Mulch had more effect on nutrient concentration in dormant plant parts after the second growing season than after the first, with the addition of sawdust under weed mat leading to significant differences for many nutrients in various plant parts as compared to weed mat alone. Total uptake of N ranged from 12 kg/ha (black weed mat) to 17 kg/ha (black weed mat over sawdust) in year 1 and averaged 33 kg/ha with no effect of mulch in year 2. Fertilizer use efficiency for N was 8% to 12% in year 1 and 42% in year 2. Uptake of other nutrients was unaffected by mulch and, depending on the year, ranged from 1.3–4.3 kg/ha P, 4.0–8.0 kg/ha K, 2.1–4.9 kg/ha Ca, and 1.0–1.5 kg/ha Mg. Each of these other nutrients were derived from the soil or decomposing roots.