Planting Potatoes
Your question, a good one, points to the importance of proper soil pH. For an answer, we consulted Cooperative Extension Services and others. These are the most succinct answers; others were similar:
• A soil test will tell you whether to use fertilizer and, if so, how much. If you don’t have a current soil test, you might apply a balanced fertilizer (for instance, 10-10-10) at a rate of about 30 pounds per 1,000 square feet, or about one pound per every 10 feet of row. Potatoes will respond well to high-fertility gardens but can produce lots of leaves and tubers that don’t keep well if plants are over-fertilized. Potatoes grown in gardens with low fertility may need fertilizer.
Ideally, fertilizer should be placed in two “bands,” each band two inches to the side of the planting and one inch below the seed piece. You can put fertilizer in the planting furrow and cover it with an inch of soil before planting the seed piece. Another option is broadcasting the fertilizer and mixing it into the soil. Either way, avoid direct contact with the seed piece. The fertilizer can cause rapid seed piece decay.
Manure is not recommended on potatoes. It tends to encourage scab development. Save the manure for other garden crops. –University of Maine
• Follow the results of a soil test to maintain a soil pH between 5.8 and 6.5 and optimal fertility levels. In gardens where potato scab is a problem, keeping the pH of the soil between 5.0 and 5.3 can significantly decrease the level of disease in susceptible varieties. If a soil test has not been taken, remember that potatoes are heavy feeders and a complete fertilizer high in phosphorus (1 tablespoon of 10-20-10 per 10 feet of row) should be added before planting. Work the fertilizer into the furrow and mix with the soil before planting. Sidedress about six weeks after planting (when tubers begin forming) with a high nitrogen fertilizer (5 tablespoons 33-0-0 per 10 feet of row). –Clemson U