My soil pH is too high. How can I reduce it into the optimum range?

In some soils the pH may be too high (> pH 7.5), usually caused by irrigation water high in bicarbonates and sodium or by applying excess amounts of lime to the soils. This can reduce the growth of plant as nutrient availability is reduced. Most crop grow best in the pH range of 5.8 to 7.0, soil pH values above 7.0 can cause plant deficiencies of important micronutrients such as zinc and manganese which are still in the soil but "tied-up" and unavailable to the plant.

Two materials commonly used for lowering soil pH are aluminum sulphate (alum) and elemental sulfur. Both materials will do the job.  Aluminum sulfate will change the soil pH instantly because the aluminum produces the acidity as soon as it dissolves in the soil. Sulfur, however, requires some time for the conversion to sulfuric acid with the aid of soil bacteria. The conversion rate of the sulfur is dependent on the fineness of the sulfur, the amount of soil moisture, soil temperature and the presence of the bacteria. Depending on these soil factors, the conversion rate of sulfur may be very slow and take several months if the conditions are not ideal. For this reason, most people use the aluminum sulfate. Both materials should be worked into the soil if possible after application to be most effective. If these materials are in contact with plant leaves as when applied to a lawn, they should be washed off the leaves immediately after application. But, b e extremely careful not to over-apply the aluminum sulfate or the sulphur, and always carry out a soil test before application, so we can advise you correctly.