ARS | Publication request: Highbush blueberry response to compost and sulfur

Submitted to: Western Nutrient Management Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 15, 2011
Publication Date: March 3, 2011
Citation: Costello, R.C., Sullivan, D.M., Bryla, D.R., Strik, B.C., Owen, J. 2011. Highbush blueberry response to compost and sulfur. Western Nutrient Management Conference Proceedings. 9:67-72.

Interpretive Summary: Blueberry plants are adapted to soils with high organic matter and acidic pH. In Oregon, highbush blueberry is usually planted in soil mixed with acidic coniferous sawdust. The sawdust improves plant growth but is becoming increasingly more expensive. Compost may be a viable alternative to sawdust but composts most suitable for blueberry have never been tested. We evaluated the response of blueberry to nine different composts mixed with soil and found that plants grew better with plant-based composts than with manure-based composts. Leaf and bark composts worked particularly well and produced as much plant growth as sawdust. Adding sulfur to the soil-compost mix (to reduce pH) increased growth by an additional 11%. Our goal is to eventually design a custom compost for blueberry that is economical for commercial production.

Technical Abstract: Highbush blueberry is adapted to soils with high organic matter and acidic pH and is often grown in Oregon with coniferous sawdust as a soil amendment or mulch. Composts could provide an alternative to sawdust, but acidification is needed to overcome high pH. Our objectives were to (i) predict the quantity of acidity needed to reduce compost pH to 4.8 (ideal for blueberry), (ii) determine compost characteristics suited for blueberry, and (iii) evaluate plant growth response and soil pH response to elemental S addition. Nine composts, including five plant-based and four manure-based materials, were titrated in the lab with sulfuric acid to estimate buffering capacity and determine the Acid Requirement Forecast (ARF; acidity required to reduce compost pH to 4.8). Compost buffering capacity averaged 0.7 mol H+/kg/compost-C per pH unit, and ARF ranged from 0 to 3.6 mol H+/kg/compost-C. Plant response to compost was evaluated in a 119-d summer growth trial. Plants were grown in 3.5-L pots filled with a 2:1 (v/v) soil:compost mix using each of the nine different composts or in a 2:1 soil:sawdust mix or in soil only. Soil pH at Day 76 in the growth trial was better correlated with compost ARF (Day 0) than starting compost pH (Day 0). Final root dry matter was negatively correlated with soil pH. Plant-based composts produced 18% greater shoot and 22% greater root growth than manure-based composts. Root and shoot dry matter of plant-based composts was not significantly different than the sawdust control, while root and shoot dry matter of manure-based composts was lower than for sawdust. Across all soil mixes, elemental S increased shoot and root dry weight by 11% and 12%, respectively, although soil pH reduction with elemental S averaged only 0.3 pH units. We conclude that laboratory testing of compost ARF can be used as a screening tool to select composts appropriate for blueberry production. Further research is needed to assess optimum elemental S rate, particle size, and incubation conditions needed to acidify compost.