In organic no-till, a cover crop is grown and allowed to get to the stage just before it will start developing seed. The cover crop is then rolled or mowed to kill it and the succeeding crop is no-till planted into the dead cover crop mulch. Weed control comes from competition and shading effect of the living cover crop and from the weed-stopping mat that the dead cover crop provides. Rolling and crimping the cover crop makes a better weed blocking mulch than mowing the cover crop. However, a rolled mulch is a little more difficult to plant into than a mowed one.
Results in the 2012 Drought
In 2012, growth and yields of both soybean and corn were adversely affected by the use of cover crops. The reasons for this are being explored. Throughout the drought, surface soil moisture was higher in plots that contained cover crop residues.
Corn that was planted into a cereal rye/hairy vetch cover crop did not germinate as well as corn planted in plots with no cover crop. Both corn growth and yields were decreased in cover crop plots. Soybean germination was not affected by the cover crop but no-till soybean plots that contained cover crops had lower yield than tilled plots.
Time of Planting Study
In order to determine the optimal time to plant corn into a rye/vetch cover crop, we tried out four different planting dates. The cover crops for each date were split into two and half was flail mowed and half was rolled down. The planting dates were:
- Corn planted while cover crop was still standing. Cover crop then rolled or mowed immediately after planting.
- Cover crop was rolled or mowed and corn was planted immediately after
- Corn was planted one week after cover crop killed.
- Corn was planted two weeks after cover crop was planted.
2012 was a season of extreme drought, so lack of water could have greatly affected the results. Data from one season showed that the best corn germination occurred when the crop was planted just before destroying the cover crop. We suspect that we did not have our planter properly set for planting corn into the thick rolled cover crop mulch and will work on planter adjustments in 2013. This may explain why germination was lower in rolled plots compared to mowed (chopped) plots. The corn planted immediately after mowing the cover crop had zero germination. We suspect that this was due to allelopathic effects from the chopped rye residue. Allelopathy is caused when an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. Rye is known to be allelopathic against other grass crops, such as corn.
Lessons learned in year one of organic no-till
- Perennial weeds, such as dock, do not die when rolled with a roller/crimper
- Cover crops may need to be rolled multiple times (we rolled two to three times) to get them to die
- If you no-till plant the opposite direction that you have rolled your cover crop, the no-till coulters will cut the cover crop, making sure it dies. If you are using the cover crop for organic weed control, this cut may let light into the row and weed pressure may increase
- Absolutely do not let your cereal rye or vetch cover crops set seed. Make sure you destroy them early enough. This is generally when pollen is shedding from rye and when vetch just begins to flower
- Start slowly and experiment with organic no-till before plunging in
- The cover crop has to be planted thick enough to hold back weeds. In drilled fields (7.5 inch row spacing) we planted a cereal rye/hairy vetch mix at 60/30 lbs/acre and got good weed control.
- In another field, we planted the same seeding rate in 15 inches rows and got almost no weed control from the cover crop
- No-till planter settings are very important and must be determined for best seed/soil contact when planting
- Flail mower blades have to be really sharp or cover crops will wrap around mower drum