Cover crops reduce soil erosion, improve soil tilth, and increase soil biological activity. Legume cover crops maintain nutrient balance in organic cropping systems because they are one of the few organic inputs that supply nitrogen (N) without phosphorus (P) or potassium (K). Cereal cover crops maintain vegetative cover in winter (to reduce soil erosion) and to take up residual soil nitrate-N from the summer crop that might otherwise leach to groundwater.

A key benefit of cover crops is their ability to supply plant-available nitrogen (PAN) for the following crop. PAN consists of ammonium-N + nitrate-N. The PAN provided by a cover crop can replace purchased N inputs such as fertilizer, compost, or manure. But to take advantage of this benefit, you need to know how to predict the PAN value of the cover crop. How much PAN is provided?

When is PAN provided? What is the best way to predict the PAN-supplying ability of various cover crop species and mixtures?