The effect of the carbon penalty was more pronounced in no-till, where the cover crop was planted into wheat stubble, than it was with tillage. As in conventional tillage, the covers were killed on March 15
As in conventional tillage, the covers were killed to March 19.
As in conventional tillage, the covers were killed to March 26.
Cover crops that grew into spring took up soil nitrates, which produced more residue, which increased the carbon penalty. Annual ryegrass had a greater carbon penalty than oats.
Cover crops that grew into spring took up soil nitrates, which produced more residue, which increased the carbon penalty. Rye and clover had a greater penalty than Austrian winter peas. (The effect of annual ryegrass on the carbon penalty may have been exaggerated, because of unusually dry weather.) The oats and Austrian winter pea winter-killed, while the annual ryegrass and rye/clover mixture continued to grow in the spring.
Slide 6 shows the importance of applying nitrogen early to feed microbes decomposing cover crops with high C/N ratios. At right, 200 lb. per acre of nitrogen was broadcast before planting following a cover of annual ryegrass. At left, the same amount of nitrogen was applied later, as a sidedress treatment.
As this photo shows, the effect of annual ryegrass on corn development was visible well past tasseling time (and will be reflected in yield). The soybeans in the foreground were not affected by the carbon penalty with any of the cover crops in the study. Keep in mind that the effect of all the cover crops probably was influenced by drought, and may be different in a wetter year.