Apparently, the annual ryegrass goes dormant when the corn canopy closes over in June, leaving the grass in shade until harvest. After harvest, sunlight sets the annual ryegrass growing again like gangbusters. According to a new article in Corn Guide, the grass soaks up residual N, P, and K going into winter. The author reports, also, that even in early years, farmers see a bump in corn production from the addition of annual ryegrass. See the full article here.