Michigan State University Extension
Soils & Soil Management - Fertilizer - 06109707
07/10/97
Potato Fertilizer Recommendations Extension Bulletin E-2220, April 1990
Maurice L. Vitosh Extension Soil Specialist Department of Crop and Soil Sciences
Calcium
Well-limed soils usually contain adequate levels of available Ca. Even soils needing lime to correct soil acidity usually contain sufficient Ca for most crops. The poor growth of plants on acid soils is usually due to excess soluble manganese, iron and/or aluminum rather than calcium deficiency. The amount of exchangeable Ca in soil is usually related to the clay content. Hence, lower exchangeable Ca levels usually occur on sandy soils.
The Ca content of soil water usually varies from 8 to 450 ppm and averages near 30 ppm. Assuming a ratio of 400 to 1 as the amount of water to produce 1 pound of dry matter, even the lowest reading of 8 ppm would supply sufficient Ca to the root. Nevertheless, localized Ca deficiency in potato tubers has been associated with internal brown spot (IBS) and increased susceptibility to soft rot disease in tubers. Limited research on Atlantic potatoes shows that gypsum (calcium sulfate) applied in the row was able to reduce IBS, though it did not reduce the incidence to an acceptable level. Calcium in these studies did not significantly affect specific gravity, hollow heart, chip color or tuber yield. Gypsum in these studies was applied at rates of 500 and 750 lb per acre. It is doubtful that the same kind of results could be obtained with low rates of Ca (less than 100 lb).
Wisconsin research has shown that potatoes may benefit from Ca fertilizer additions when soils test less than 700 lb of exchangeable Ca per acre. Most of these soils will also benefit from lime (calcium carbonate), which also raises the soil pH. Further research in Michigan is needed to determine when supplemental Ca should be applied, how much and what source. With our present knowledge, it is difficult to recommend supplemental Ca for tuber quality enhancement as a general practice.