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Research Project: Integrated Water and Nutrient Management Systems for Sustainable and High-Quality Production of Temperate Fruit and Nursery Crops

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Title: Chemigation with micronized sulfur rapidly reduces soil pH in northern highbush blueberry

item ALMUTAIRI, KHALID - Oregon State University
item MACHADO, RUI - University Of Evora
item Bryla, David
item STRIK, BERNADINE - Oregon State University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2017
Publication Date: 11/1/2017
Citation: Almutairi, K.F., Machado, R.M., Bryla, D.R., Strik, B.C. 2017. Chemigation with micronized sulfur rapidly reduces soil pH in northern highbush blueberry. HortScience. 52(10):1413-1418.

Interpretive Summary: Northern highbush blueberry is adapted to acidic soil conditions and often grows poorly when soil pH is greater than 5.5. When soil pH is high, growers will usually mix prilled (granular) elemental sulfur into the soil prior to planting (converted to sulfuric acid by soil bacteria) and, if needed, inject acid into the irrigation water after planting. These practices are effective but often expensive and time consuming. Here, we examined the potential of applying micronized sulfur as an alternative to reduce soil pH in blueberry. The product was mixed with water and injected through the drip irrigation system (chemigation). Currently, there are several micronized S products on the market labelled for chemigation. It is reasonable to expect that applying sulfur through a drip system would reduce soil pH faster and require less product than conventional applications of prilled sulfur, because during chemigation, the sulfur would concentrate beneath the drip emitter where many of the roots are found and where soil conditions are moist and favorable for rapid bacterial transformation of S to sulfuric acid. Micronized sulfur was applied through the drip system before planting (to evaluate its use as a pre-plant amendment) and after planting (to assess its value for reducing soil pH once the field was established). The findings indicated that chemigation with micronized could be used to quickly reduce soil pH in a blueberry field. However, it was less effective and more time consuming than using prilled S prior to planting. Therefore, S chemigation may be most useful when soil pH is too high after planting. The practice is less expensive and safer than using acid to correct high soil pH problems and is a convenient alternative for both conventional and organic blueberry production.

Technical Abstract: Northern highbush blueberry is adapted to low soil pH in the range of 4.5–5.5. When pH is higher, soil is usually acidified by incorporating elemental sulfur (S) prior to planting. A study was conducted to determine the potential of applying micronized S by chemigation through the drip system to reduce high soil pH in a new planting of ‘Duke’ blueberry. The S was mixed with water and injected weekly for ˜2 months prior to planting (July–Sept.) and again at 2 years after planting (Aug.–Oct.) at rates of 0, 50, 100 and 150 kg/ha S per year. Each treatment was compared to the conventional practice of incorporating prilled elemental S into the soil prior to planting (two applications of 750 kg/ha of S each in July and Oct.). Within a month of the first application of S, chemigation reduced soil pH from an average of 6.6 with no S to 6.1 with 50 kg/ha of S and 5.8 with 100 or 150 kg/ha of S. However, reductions in pH were short-term, and by May of the following year, soil pH averaged 6.7, 6.5, 6.2, and 6.1 with each increasing rate of S chemigation, respectively. Soil pH in the conventional treatment, in comparison, averaged 6.6 a month after the first application and 6.3 the following May. In July of the second year after planting, soil pH ranged from an average of 6.4 with no S to 6.2 with 150 kg/ha of S and 5.5 with prilled S. Soil pH declined thereafter to as low as 5.9 with post-planting S chemigation and, at lower depths (10–30 cm), was similar to the conventional treatment. The findings indicate that S chemigation can be used to quickly reduce soil pH following planting and, therefore, may be a useful practice to correct high pH problems in established northern highbush blueberry fields. However, it was less effective and more time consuming than applying prilled elemental S prior to planting.