Adoption of cover crops in Pennsylvania’s Chesapeake Bay watershed

Abstract

Cover cropping is considered a very cost-effective practice to reduce losses of nitrogen (N) from cropland to surface waters, as well as mobile nutrients in the soil profile prone to being lost to ground water sources. Cover crops are an important component of states’ commitment to improve water quality in the Chesapeake Bay. Since 2016, annual cover crop transect surveys have been performed in Pennsylvania’s Chesapeake Bay watershed. The surveys show that cover crops were used on 39% of the annual crop area in the period 2016 to 2021, much higher than average cover crop use in the United States (5%). About two-thirds of the cover crop area is “commodity cover crops” that are harvested (which included both grain and forage harvesting in the surveys), while the other one-third is “traditional cover crops” that are not harvested. It appears that high cover crop adoption in Pennsylvania without generous subsidy payments is due in great part to their use for forage. However, at the moment, commodity cover crops receive no credit for pollutant reduction in the Chesapeake Bay Model if fall nutrients are applied, which means approximately two-thirds of cover crop implementation in Pennsylvania does not count toward nutrient pollution reduction to the Chesapeake Bay. Further, transect surveys are not considered a valid (or only partial) method of practice implementation and the present results are therefore not included when determining if states meet Total Maximum Daily Load (TMDL) limits. Considering their importance, the contribution of commodity cover crops to nutrient and sediment loss reduction from cropland needs to be better understood. Specifically, our study revealed the need to (1) clarify in Chesapeake Bay Model documentation that commodity cover crops include those harvested for forage besides those harvested for grain; (2) develop a tracking mechanism so that nutrient reduction credit from commodity cover crops can be recognized in the Chesapeake Bay Model; and (3) to review whether the lower N reduction credit from commodity cover crops than for traditional cover crops and lower credit for early planting are justified.