254-Soil pH Management

Fact Sheet No. 254


Prepared by Lily Calderwood, PhD and David E. Yarborough, PhD
Extension Wild Blueberry Specialists

Soil Sampling for pH
To take one sample, collect 15 to 20 soil cores at a three to six-inch depth and mix them together in a bucket. Be sure sample is a representative sample from all parts of your field. If field conditions are very different, take entirely separate samples.

Summary tips: 1. Wild blueberries are well adapted to a low pH environment. 2. Reducing pH will favor wild blueberry while and reducing weeds, especially grasses. 3. Apply 100 lb sulfur/acre for each 0.1 pH unit reduction. 4. Sulfur is less expensive than an herbicide. 5. It can take 2-3 years to see a reduction in pH levels and therefore weed control. Using sulfur takes longer but also lasts longer.Put each sample into a Maine Soil Testing Lab box and send it to:
Maine Soil Testing Services
5722 Deering Hall
Orono, ME 04469
207.581.2945 or 207.581.2934

Indicate that your sample is wild blueberry soil and that you only require pH analysis. The cost is currently $12.00. For more than pH testing, visit the 2019 Price Page. The analysis report that you receive will give recommendations on the amount of sulfur needed to reduce your pH appropriately.

Fields differ in organic matter (OM) and cation exchange capacity (CEC) so pH change will vary from field to field. Re-sampling the field each year is necessary to determine what change has occurred and will help you to decide if a reapplication of sulfur is required. Note: Take leaf samples to determine your plant’s fertilizer needs. Excess fertilizer will feed weeds and reduce blueberry yield and quality.

Sulfur Applications to Wild Blueberry

Do not apply more than 1000 lb/acre of sulfur in any given year.
Do not apply sulfur to saturated soil or wet leaves as you could burn your plants.

Sulfur is an effective treatment for reducing soil pH to control weeds in wild blueberry fields. Experiments conducted in over thirteen locations in Maine from 2000 to 2005, sulfur applied at 500 or 1000 pounds per acre was effective in reducing the soil pH one-half to one pH unit. When the target pH (4.0) was reached, a reduction in weeds, especially grasses, was observed. When sulfur was applied with herbicide (Sinbar or Velpar) additional suppression was obtained. The application of 1000 pounds per acre to an organic field reduced the pH from 5.0 to 4.0 and resulted in a decrease in weeds two years after the application. Yield in the organic field was doubled by burning vs. mowing and with the use of sulfur on mowed areas. Importantly, when burning was combined with sulfur application, blueberry yield increased three-fold.

How does it work?
By reducing the pH, a hostile environment for weeds is created. The wild blueberry has evolved in this acidic environment and partners with mychorrhizae fungi that scavenge for nutrients and shuttle them back to the blueberry. Sulfur will control many but not all weeds. Some plants such as sweet fern and lamb kill are well adapted to the same acidic soils as the blueberry. In general, it takes two to three years for a sulfur application to reduce the soil pH and it takes about 100 pounds of sulfur pellets to reduce the soil pH 0.1 units. In our on-farm research, there was a difference in the speed at which pH dropped and in the length of time that the pH stayed reduced. This is related to differences in organic matter content and Cation Exchange Capacity of soil from one field to the next.

Granular Sulfur
Figure 1. Granular sulfur (SO4, 90%)

Sulfur comes in the form of a pellet and looks like a small split pea (Figure 1). It can be applied with a conventional fertilizer spreader or air assist spreader. It is important to get an even application of the sulfur, making the air assist spreader most effective. If you do use a Vicon type granular fertilizer spreader, you will need to cut your application rate in half and then overlap your application by 50% in order to get an even application on the field. The goal is to reduce the soil pH in your field to a pH of 4.0. You will have to monitor the soil pH on your field and may have to reapply sulfur after six years to maintain the lower pH level. Initially the application will be more expensive than a single herbicide application but sulfur will last longer than an herbicide application.

Timing of Application
It is usually best to take soil samples at the same time as leaf samples, which is at “tip-die back stage” in early July. However, soil sampling in the fall or spring is fine as long as yearly, comparative soil samples are also taken at the same time of year. Ideally, sulfur should be applied in the spring after pruning and before blueberry leaves emerge. It could also be applied other times of the year EXCEPT during the following conditions:

  • Frozen ground
  • Saturated soil with standing water
  • Wet blueberry leaves

Flowering weeds in blueberry field

 


Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 1998, 2008, 2013, 2019

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