Plots in no-till for the past 28 years produced corn yields this year of 234.8 bushels per acre in a tillage study on the University of Nebraska's Rogers Memorial Farm. That yield was 20 bushels to the acre greater than the next highest yields raised on plots that were plowed and disced twice.
These dryland research and demonstration plots were started as a soybean/grain sorghum rotation and are now in a corn/soybean rotation. Across the years, they have shown that continuous no-till builds soil structure, usually has the highest yield, and is the most profitable, says Paul Jasa, University of Nebraska ag engineer.
Other corn yields included 214 bushels per acre for disced with a cover crop; 209.8 for no-till with a cover crop, 209.7 for disc-disc; and 205.5 for chisel-disc.
The continuous no-tilled plot was also the highest yielder for soybeans at 54.3 bushels per acre, just barely ahead of the no-tilled cover crop plot of 54 bushels per acre. Other soybean yields included 51.8 for disc-disc; 50.8 for chisel-disc; 49.0 for disc with cover crop; and 48.2 for plow-disc-disc.
Jasa says the yields from 2009 showed that the crops did quite well, even in a year with below-normal rainfall. The season started with a full soil-moisture profile because of good rains after harvest last fall. As the crop was getting established, only 1.7 inches fell in April and 1.8 inches came in May.
Rainfall was more than 6 inches below normal through the growing season with only 1.4 inches falling between July 4 and Aug. 15, during the corn-ear elongation period and beginning soybean-pod development.
"Fortunately, there was enough stored soil moisture to carry the crops through this dry part of the season," Jasa says. "About 3 inches came later in August and only 1.7 fell in September, good for the corn, but not enough for complete pod fill of the soybeans.
"While coming too late to help the yields, about 4.6 inches of rain fell in October which, along with the cool weather, slowed dry down and delayed harvest.
After harvest in 2007, a cereal rye cover crop was drilled into one of the no-till treatments (no-till cultivated in the past) and one of the disc treatments (single disc in the past) to intensify the cropping diversity by adding a winter annual grass to the system. Jasa says cover crops use some soil moisture and "harvest" sunlight and carbon dioxide during the off-season to add biomass to the soil system.
"While this builds soil in the long term, it also allows for evaluation of the effects on yield," he says.
In the no-till corn treatment, the cover crop was sprayed and killed when the rye was about 2 inches tall (about 2.5 weeks before planting corn). In the disc treatment, two discings were used to kill the cover crop, one in mid-April and the other at the end of April.
The corn and soybeans were both planted May 3. The rye cover crop in the no-till soybean treatment was sprayed and killed about 2 weeks later when the rye was just beginning to head.
"Similar to 2008, the use of the fall-seeded rye cover crop on the soybean residue decreased the 2009 corn yield for the no-till treatment, resulting in a yield similar to the that of the disc treatment without a cover crop," Jasa says. "However, the cover crop on the disc treatment increased the corn yield compared to the disc treatment without a cover crop. The rye cover crop on the corn residue decreased the soybean yields slightly for both the no-till and disc treatments.
After harvest, a cereal rye cover crop was again drilled into the same two treatments. This use of cover crops will continue and add a new dimension to the tillage study, Jasa says, allowing a view of how the extra roots and biomass affect the soil system.
"The continued use of no-till has improved soil structure and protects the soil surface with residue," Jasa adds. "Properly managed cover crops will add to that by improving biological diversity and adding biomass in the off-season."