The Impact of Underseeding and Overseeding Cover Crops on the Agronomic Performance of Soybean and Canola in the Northeast.

Oilseed production in the Northeast is a challenge due to a very short growing season.  Soybean in particular, is harvested very late and contributes very little organic matter to the soil in potato-based cropping systems.  These factors combined, leave agricultural soil susceptible to erosion during winter months.  A study was conducted to evaluate underseeding or overseeding cover crops into oilseeds, and the effect on the agronomic performance of both the main crop and the cover crop.  Both canola and soybean were either underseeded or overseeded with red clover, white clover, or cereal rye.  Underseeding occurred in the spring at the same time as the main crop was planted.  Overseeding occurred later in the season and corresponded with soybean leaf drop.  Herbicide application was also included as a factor to evaluate whether there was a herbicide interaction with main crop or cover crop performance.  Overall, yields were highly variable depending on the identity of the intercrop, and the timing of seeding the intercrop.   Canola yields ranged from 1200 to 1700 kg ha^-1; soybean yields ranged from 800 to 2100 kg ha^-1.  In both cases, the lowest yielding treatments were those underseeded with cereal rye.  For canola, there were no significant differences in yield between treatments including underseeded and overseeded white clover or red clover and the control. However cereal rye particularly when underseeded with the main crop resulted in significantly lower yields compared to the control. For soybean, yields were significantly lower in underseeded plots compared with the control for most forage species except underseeded red clover.  Also, the distance to the bottom pod in soybean was significantly higher compared to the control.  At present, it would appear that there is a potential for underseeding canola, and there is also a potential for overseeding soybean.    More work is required to determine optimal seeding rates and dates for both underseeding and overseeding in oilseed crops.