Looking at Crimson Clover in Cover Crop Mix with Annual Ryegrass
Crimson clover’s peak potential to fix Nitrogen is just before it blooms. It can fix the most nitrogen (up to 135b/ac) in the soil at that time. But in a normal weather year, Central Midwest growers would terminate the crimson clover in mid April, ahead of planting corn. This is well before bloom, thus limiting the amount of N actually produced.
This spring, being so late, Indiana grower Mike Starkey decided to leave the cover crop on his field a month longer than normal. The cover crop mix was crimson clover, annual ryegrass, Austrian winter pea and dicon radish. As you can see in the photos below (5/19/14), the clover is in full bloom. Purdue University students were there taking samples on the 80 acre parcel to determine the N content.
While many in the Midwest experienced a tough cover crop year because of the harsh winter, this parcel fared well due to the tree line which acted as a windbreak. A minus 20 to minus 30 degree windchill with no snow cover seems to be the threshold at which winterkill occurs. Many areas had significant snow but the wind blew the snow off of some areas.