Effect of Seeding Date on Interseeded Winter Annual Cover Crop Growth and Nitrogen Uptake.

Thomason, Black, S. Reiter, R. Clark, PH Davis, M. Reiter

Winter cover crops have the potential to reduce the impact of agricultural production on the surrounding ecosystem in the mid-Atlantic USA, including the Chesapeake Bay.  However the seasonality of cash crop harvest is one major issue slowing the expansion of cover crops.  The objectives of this study were to evaluate broadcast-seeded winter cover crop biomass production, nitrogen (N) uptake, and residual soil N as affected by date of cover crop seeding.  Field experiments were conducted in six total locations in Virginia in 2012-13 and 2013-14.  Treatments consisted of barley (Hordeum vulgare L.), rye (Secale cereale L.), rye+forage radish (Raphanus sativus L.), and rye+hairy vetch (Vicia villosa L.) hand-broadcast into standing crop beginning in early September and each two weeks afterward in a split plot design with four replications.  Aboveground biomass was hand clipped from a 0.5 m-2 area in each treatment in early December and in spring, just prior to killing the cover crop to estimate fall and total biomass, respectively.  Crop samples were dried in a forced air oven at 60°C for 48 hr and then ground to pass a 2 mm screen using a Wiley (Thomas Scientific, Swedesboro, NJ) sample mill and total carbon (C )and N determined by dry combustion (Leco Corp., St. Joseph, MI).  Nitrogen uptake was determined as the product of dry matter yield and tissue N concentration.  Initial results indicate a rapid decrease in fall biomass when seeding after early October at all sites.