Michigan State University Extension
Soils & Soil Management - Fertilizer - 06109702
07/10/97
Potato Fertilizer Recommendations Extension Bulletin E-2220, April 1990
Maurice L. Vitosh Extension Soil Specialist Department of Crop and Soil Sciences
Soil acidity is extremely important to plant growth and nutrient availability. Potatoes grow best at pH 5.2 to 6.5. Below pH 5.0, aluminum and manganese toxicities occur, reducing both growth and tuber yield.
The lime requirement of acid soils is determined by measuring both solution and exchangeable hydrogen and aluminum. At Michigan State University, the SMP buffer method is used to measure the lime requirement. The degree of acidity is reported on the soil test report as lime index.
Potatoes should be limed to pH 6.0. Table 1 gives lime recommendations based on the lime index and a 9-inch plow layer. Growers need to take several precautions to prevent potato scab, which is often promoted by the addition of limestone. Growers are advised to use scab-tolerant varieties when they are available. Do not apply more than 1 ton of lime within 6 months of potato planting, and do not exceed 2 tons of lime in any one application. ==================================================== Table 1. Tons of limestone needed to raise the soil pH of mineral soils to pH 6.0 as determined by the lime index method.
Lime Lime recommendation (9-inch plow depth) index tons/acre ---------------------------------------------------- 69 0.0 68 1.2 67 1.9 66 2.7 65 3.5 64 4.3 63 5.1
To convert lime recommendations to a depth of plowing other than 9 inches, divide the above rates by 9 and multiply by the depth of plowing (number of inches). ==================================================== Apply lime in the fall after potato harvest and preferably one or more years before potatoes are to be grown in the rotation. Use finely ground limestone when it is available large granules of limestone have been known to cause localized scab infections.