The Shenandoah Valley of Virginia and some other regions produce more manure nutrients than local crops need. This manure has traditionally been applied to row crops and overapplication has led to soil-test phosphorus (P) being well above agronomic optimum in many cases. In 2008, it was estimated that nutrient-management regulations now require that approximately 85 percent of poultry litter be applied off poultry farms, as they do not have sufficient land to beneficially recycle their manure nutrients.

There are many, many factors that could cause either of these statements to be true: year-to-year weather variation, yield potential differences in and between fields, planting date differences, etc. (first published March 2019, last reviewed March 2024)