Using Gypsum to Reduce Tuber Rot and Increase Potato Yields on Sandy Loam Soils.

Calcium (Ca) and sulfur (S) may significantly impact white potato (Solanum tuberosum) tuber quality and yield in the Mid-Atlantic. A field trial was initiated on a Bojac sandy loam using ‘Superior’ white potatoes in summer 2010. Gypsum was applied at 1120, 2240, 3360, and 4480 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. Soft rot (Erwinia carotovora ss. carotovora) and Pythium leak (Pythium sp.) occurred naturally in this trial causing tuber rots in the field. Potato tubers were harvested using a mechanized potato harvester and graded for marketability.  Gypsum applications reduced tuber rot in 2010 and 2011 and increased total marketable yield. Sulfur applications alone did not impact total yield, but S applications via gypsum did reduce tuber rot in 2011. Little tuber rot incidence occurred in 2012 or 2013 and treatments had no significant impact on rot or yield. Overall, gypsum applications may be beneficial in years with high tuber rot incidence to reduce rot and increase marketable yield for potatoes grown in Mid-Atlantic sandy loam soils.