Amending Sandy Soil with Biochar Promotes Plant Growth and Root Colonization by Mycorrhizal Fungi in Highbush Blueberry

Abstract

<jats:p>Biochar, a carbon-rich, fine-grained residue obtained from pyrolysis of biomass, is known to improve soil conditions and to suppress infection by soilborne pathogens. However, its use as a soil amendment has received relatively little attention by the horticulture industry. Two 12-week experiments were conducted in a greenhouse to determine the potential of using biochar, produced from mixed conifers during conversion of wood to energy, as a soil amendment for highbush blueberry (<jats:italic>Vaccinium</jats:italic> hybrid ‘Legacy’). Plants in the first experiment were fertilized once a week with a complete fertilizer solution, whereas those the in the second experiment were fertilized once a month with a solution of ammonium sulfate. In both cases, the plants received the same amount of N in total and were grown in pots filled with unamended soil (sandy loam) or soil amended at rates of 10% or 20%, by volume, with biochar or a 4:1 mix of biochar and bokashi (biochar-bokashi). The bokashi was produced from fermented rice (<jats:italic>Oryza sativa</jats:italic> L.) bran and was added to increase nutrients in the amendment. Half of the plants in each soil treatment were inoculated with <jats:italic>Phytophthora cinnamomi</jats:italic> Rands, which causes root rot in blueberry. Although pH of the raw biochar was high (8.5), soil pH averaged 4.5 to 5.5 in each treatment. In the absence of <jats:italic>P. cinnamomi</jats:italic>, plants grown with 20% biochar or 10% or 20% biochar-bokashi had greater leaf area and 30% to 70% more total dry weight than those grown with 10% biochar or in unamended soil. Biochar also improved soil aggregation and increased root colonization by ericoid mycorrhizal fungi. The percentage of roots colonized by mycorrhizal fungi was 54% to 94% in plants grown with the amendments, but was ≤10% in those grown in unamended soil. Plants inoculated with <jats:italic>P. cinnamomi</jats:italic> were stunted and showed typical symptoms of root rot. Root infection by the pathogen was unaffected by biochar or biochar-bokashi and negated any growth benefits of the amendments. Overall, amending soil with biochar appears to be a promising means of promoting plant growth and mycorrhizal colonization in blueberry, but it may not suppress phytophthora root rot.</jats:p>

Biochar as an Alternative Soil Amendment for Establishment of Northern Highbush Blueberry

“…Biochar is known to act as a liming agent (Trippe et al, 2015). However, we did not find this to be the case in this or our previous study with biochar for blueberry (Sales et al, 2020). In both cases, the biochar was produced from wood debris obtained from mixed conifer species.…”

“…To increase organic matter, growers often incorporate bark or sawdust into the soil before planting blueberry, as well as use them as mulch afterward; however, the cost of these materials is increasing and availability is limited in many regions (Larco et al, 2013a). Recently, we conducted greenhouse experiments to determine whether biochar could be used as an alternative amendment for highbush blueberry (Vaccinium hybrid) (Sales et al, 2020). The biochar in this case was produced from mixed conifers during conversion of wood to energy.…”

“…Within 12 weeks, the plants grown in soil with the biochar were larger and more heavily colonized by ericoid mycorrhizal fungi than those grown in unamended soil. Additional growth and colonization were achieved in a second experiment conducted under N limited conditions by adding bokashi (a mix of fermented wheat bran, molasses, and naturally occurring microbes) to the biochar (Sales et al, 2020). With or without bokashi, the biochar increased soil pH by 0.3 units or less, even when it was incorporated at a rate as high as 20% by volume.…”

A Review for Southern Highbush Blueberry Alternative Production Systems

“…Agricultural soils rarely meet these requirements. Thus, growers traditionally prepare fields with the addition of sulfur, organic matter, or other amendments [69][70][71]. Even with these inputs, SHB soil preferences limit the areas where it can be planted.…”

Biochar in temperate soils: opportunities and challenges

“…Another study, where the authors evaluated the effect of eight biochar amendments on the severity of soybean root rot caused by Fusarium virguliforme in a silty clay loam, showed no evidence of systemic and indirect effects of biochar on severity of soybean root rot (Rogovska et al 2017). Sales et al (2020) also found no effect on the suppression of phytophthora root rot of highbush blueberry (Vaccinium hybrid 'Legacy') in a sandy soil amended with a commercial biochar manufactured from mixed conifers and inoculated with Phytophthora cinnamomic. The root infection by P. cinnamomi also increased with the increase biochar application rate and this effect could partly be explained by the organic compounds found in biochar.…”