Impact of Gypsum on Yield and Tuber Rot for White Potatoes in the Mid-Atlantic.

Calcium (Ca) and sulfur (S) may significantly impact white potato (Solanum tuberosum) tuber quality and yield in the Mid-Atlantic. Eastern Shore of Virginia soils are naturally deficient in S and S depositions have decreased due to reductions in acid rain; warranting additions of S fertilizer. Similarly, sandy loam soils often test low for Ca and soil test values continue to decrease as lime use is reduced due to proper fertility management, a desired low pH for potato production, and reductions in acid rain. Studies indicated that use of S and Ca containing products, such as gypsum, not only increased yield but reduced tuber rot and increased tuber quality.  A field trial was initiated on a Bojac sandy loam using ‘Superior’ white potatoes in summer 2010. Gypsum was applied at 454, 907, 1361, and 1841 kg ha^-1, giving effective S application rates of 188, 376, 564, and 753 kg S ha^-1 and Ca application rates of 252, 504, 756, and 1008 kg Ca ha^-1. Sulfur rates comparable to the gypsum application were also applied using elemental sulfur along with separate treatments of 0, 28, 56, and 112 kg S ha^-1. Erwinia carotovora ss. carotovora and Pythium sp. occurred naturally in this trial causing tuber rots in the field. Potato tubers were harvested and graded for marketability using a mechanized potato harvester. In 2010, no Ca or S treatment significantly decreased tuber rot (average = 12.9%), increased marketable yield (average = 19,143 kg tubers ha^-1), nor increased total yield (average = 21,535 kg tubers ha^-1). This study will be continued in summers 2011 and 2012 to determine if S and Ca fertilization would increase tuber yields and reduce tuber rots for Mid-Atlantic sandy loam soils.