Amy Shober, Extension Nutrient Management and Environmental Quality Specialist; ashober@udel.eduand Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu

Hairy vetch (left) and crimson clover (right) mixed with rye cover crop plots.

Small grains or legumes are commonly planted as cover crops in Delaware. While small grains are good at scavenging left over soil nitrogen (N) in the fall, they are not as likely as a legume cover crop to release that N early in the spring. It is helpful to remember that the C:N ratio of a cover crop can predict N availability to crops in the spring. A cover crop with a C:N < 20 at termination will be easily broken down by soil microbes and release N to the soil. In contrast, a cover crop with a C:N >30 at termination could result in tie up (immobilization) of soil N. If N is tied up by microbes, it will not be available for the emerging crop in the spring but may be available later in the season as that residue breaks down. Continue reading