Cultural Management - 254-Cultural Management pH
Fact Sheet No. 254
Prepared by David E. Yarborough, Extension Blueberry Specialist, The University of Maine, Orono, ME 04469. June 1998. Revised and expanded December 2008.
- Wild blueberries are well adapted to a low pH environment.
- Reducing the pH in your soil gives the advantage to the wild blueberry over many weeds but will not suppress all weeds.
- Sulfur at approximately 100 lb/acre for a reduction of 0.1 pH unit is less expensive than an herbicide.
- Change in pH may take several years to be completed. Results take longer to obtain but last longer.
Take 15 to 20 soil cores to a 3 to 6 inch depth. Be sure sample is a representative sample from all parts of your field, if field conditions are different take a separate sample.
Put mixed sample in soil box and send to:
Maine Soil Testing Services
5722 Deering Hall
Orono, ME 04469-5722
(207) 581-2945 or 581-2934
Indicate it is wild blueberry soil and ask for pH only, the cost is currently $7.00 (discounted price for blueberry growers only), but is subject to change. Visit http://anlab.umesci.maine.edu/soillab_files/prices/index.html for costs of other sample tests.
Analysis report will give recommendations on amounts of sulfur to reduce pH.
Fields differ in organic matter and cation exchange capacity so pH change will vary from field to field. Resampling the field each year is necessary to determine what change has occurred and to determine the need to apply more sulfur.
Note: Be sure and take leaf samples to determine your plants fertilizer needs, excess fertilizer will feed weeds and reduce your yields.
Caution: do not apply more than 1000 lb/a of sulfur in any given year or apply when ground is saturated or injury to blueberries could result.
Sulfur is an effective treatment for reducing soil pH to control weeds in wild blueberry fields
In experiments conducted 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 level of pH 4.0 was reached we found a reduction in weeds, especially grasses and when used with the herbicides Sinbar or Velpar additional suppression was obtained by the sulfur. 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. The yields in the organic field were doubled by burning vs. mowing and also doubled with the use of sulfur on the mowed areas, but when burning and sulfur application was combined the yield was increased by three fold. The sulfur will reduce the availability of soil nutrients for the weeds but allows the blueberries to grow as well as at a higher pH because wild blueberries are well adapted to acid soil. This method will not control all weeds, as there are other weeds in you fields which are also well adapted to acid soils, but it will control many competitive weeds that reduce blueberry yield.
In general it takes two to three years for the sulfur application to reduce the soil pH and it takes about 100 pounds of sulfur pellets to reduce the soil pH 0.1 units. There is a difference in the rate of reduction and length of time the pH was reduced. This is related to differences in the organic matter (OM) and the Cation Exchange Capacity (CEC), so that a soil sample on the field you want to treat is needed initially to determine your starting pH and over time to monitor its progress. The goal is to reduce the soil pH in you field to a pH of 4.0. You will have to monitor the soil pH on your field and may have to retreat with sulfur after six years to maintain the lower pH level. So this treatment may be initially more expensive than an herbicide application but the effect is much more long lasting.
The soil test is usually taken at the same time as leaf test samples, at tip-die back stage of blueberry growth in July of the non-crop year, but if you take the soil sample in the spring continue to take the sample at the same time of year to get an accurate comparison of the samples. Take a random sample of 30 or more places in your field. Take a sample of the top three to four inches of soil, put it in a container and mix it well. Send a sample of this soil to the soil testing lab and request pH only. The goal is to reduce the soil pH in your field to 4.0, so if it is at 4.5 then it would take 500 pounds per acre and if it is at 5.0 it would take 1000 pounds per acre. It will take two to three years for the pH to be reduced and it may begin to rise five to six years after the initial application.
We applied the sulfur in the spring after pruning but it could be applied other times of the year, except if the ground is frozen, or if the soil is saturated with standing water or if the plant leaves are wet. Applying it preemergence in the spring to pruned plants would have the least potential for any blueberry plant injury.
Sulfur comes in the form of a pellet and looks like a small split pea and may be applied with a conventional fertilizer spreader. It is important to get an even application of the sulfur, so an air assist spreader is the best way to apply it to your field. 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.
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
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