Last week’s USDA Quarterly Stocks report revealed that farmers are holding 36 percent more corn in on-farm storage than a year earlier. One rule of thumb is for farmers to calculate their break-even point and then market their crop over the marketing year. The old calculus, before South America became a counter-cyclical supplier, was for prices to be lowest at the start of the marketing year and then rise as supplies are depleted. That model is clearly discredited as corn prices now decline in the last few weeks of the marketing year.   Farmers could try to continue holding on to their stocks, awaiting and hoping the market will eventually add a weather premium. Many larger farms are well capitalized for such a strategy. Bu...