April 3, 2009

Cover Crops Add a New Dimension

Figure 1. A cereal rye cover crop grows in corn residue, feeding the soil biological life. The photo, taken this week, shows little corn residue remaining from the more than 210 bushel per acre corn grown last year. Soybeans will be planted in this continuous no-till treatment. The biological activity in a continuous no-till system cycles most of the nutrients and carbon from the residue back into the soil system for the next crop.

A tillage study was established in 1981 at the University of Nebraska Rogers Memorial Farm, 10 miles east of Lincoln, to gain experience with various tillage systems. 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.

2008 Plot Record

The yields from 2008 showed that the crops did quite well, even in a year with a cool, wet spring. The season started with a full soil moisture profile at planting. As the crop was getting established, about 4.9 inches of rain fell in May. Another 8.5 inches fell in June and 2.8 inches more came in July. Then it turned dry in August with only 1.2 inches during the corn grain fill period. Fortunately, there was enough stored soil moisture to carry the corn through the rest of the season. In September about 2.7 inches of rain fell, helping the soybeans to fill the pods. As in most past years, the no-till plots had the highest yields and the best profitability since they didn't have any tillage costs.

Rye Cover Crop Added

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 disk treatments (disk in the past) to intensify the cropping diversity by adding a winter annual grass to the system (Figure 1). These cover crops will 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.

In the no-till treatment, the cover crop was sprayed and killed when the rye was about 5 inches tall (about 2.5 weeks before planting corn). In the disk treatment, two diskings were used to kill the cover crop, one in mid April and the other at the end of April. The corn was planted on April 30 and the soybeans on May 6.

The use of the fall-seeded rye cover crop on the soybean residue decreased the corn yields for both the disk and no-till treatments (Table 1). However, the cover crop on the corn residue increased the soybean yields for both treatments. With all the rainfall that came in June, it's not likely the yield loss in the corn resulted from the rye using valuable soil moisture.

Though sprayed more than two weeks before planting corn, the rye was slow to die in the cool, wet spring weather and may have affected early corn growth. Soybeans, being a broadleaf crop, are less likely to be affected by the dying rye plants. While rye was selected for convenience and quick growth, perhaps a broadleaf winter annual cover crop should be used before corn production instead.

After harvest in 2008, 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, allowing us to look at 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. Properly managed cover crops will add to that by improving biological diversity and adding biomass in the off-season.

Paul Jasa
Extension Engineer