Trials reveal cover crop distinctions
Cover crop plantings of Berseem and Crimson clover and small grains during the first half of August during the past three years in Sheboygan County have provided insights on differences in dry matter yields of those crops and subsequent corn crops, on the carbon to nitrogen ratios in the soils, and on response to nitrogen applications.
The details of those projects were reported by the county's Extension Service crops and soils agent Mike Ballweg at a forum on soil health and cover crops sponsored by the soil and water conservation and Extension Service offices in Manitowoc County, the Natural Resources Conservation Service, In-Depth Agronomy, Soaring Eagle Dairy and the Wisconsin Farmers Union.
Additional financial support for the forum was provided by Country Visions Cooperative, Byron Seeds, Poplar Farms, Quality Roasting, Legacy Seeds, La Crosse Seeds and Deer Creek Seed.
The cover crop study in Sheboygan County started in 2013 on the Nick Kleiber farm near Waldo, where acreage that was a victim of prevented planting during the first part of the growing season was seeded with 12 to 15 pounds of the clover seed per acre along with 50 pounds of oats, Ballweg pointed out. The plot, which was set up in four replications with eight nitrogen rates, was seeded on Aug. 9.
For 2014 and 2015, the project moved to the Dennis Roehrborn family's farm near Johnsonville and fields from which winter wheat was harvested. Berseem and Crimson clovers were planted at 10 and 11 pounds per acre with 60 pounds of barley in 2014 and then at 15 pounds for each of the clovers in 2015 along with 60 pounds of barley. The respective seeding dates were Aug. 15 and 12.
Ballweg emphasized that about 40 percent of the growing degree days and rainfall occur after Aug. 1. Following vegetable crops or wheat, that leaves plenty of time to grow clovers and small grains that cannot only serve as a late season cover crop for that land but can also provide forage for grazing, ensiling, baling or stockpiling.
That scenario played out very well in 2013 on the Kleiber farm with vigorous growth of all three species, reaching 3.77 dry matter tons per acre for the barley, 3.32 tons for Crimson clover and 2.68 tons for the Berseem clover. Ballweg remarked that an ideal set of circumstances resulted in the amount of biomass that he wouldn't count on to be typical.
Among Ballweg's observations in the first year with clover varieties that are seldom grown in northern climates were that Berseem grew like and resembled an annual alfalfa, that the Crimson was shorter and more dense, that the Crimson was more cold tolerant and could possibly survive the winter with a good snow cover and that the amount of residue left in the spring of 2014 was not a problem for no-till planting.
On the Roehrborn farm in 2014, the cover crops suffered somewhat from excess rainfall a few weeks after they were planted and the end of growing season biomass was only 30 to 40 percent of what they were the previous year. Those numbers were only slightly higher in the autumn of 2015 with the barley, whose heads stood at about 36 inches, posting a per acre dry matter total of 1.76 tons.
One significant difference that Ballweg noted in 2015 was in the nodules on the clovers. The Berseem was very well noduled, while the Crimson was not.
Nitrogen and carbon
Consistent with cover crop studies elsewhere, the soil nitrogen residual levels at one and two foot depths remained highest where no cover crops were planted, were lowest with the small grains and the restricted growth in 2014 and were slightly higher with the nitrogen-fixing clovers, Ballweg reported.
Tests of the carbon to nitrogen ratio taken in November confirmed that the barley and oats tied up the nitrogen in their biomass, Ballweg indicated. That put their ratios above the neutral 25 to 1 ratio while the ratios with the clover were comfortably below the neutral ratio.
As is also born out in other research studies, the supplementing of nitrogen pointed to having 160 pounds per acre as the ideal with very little corn yield response in 2015 with higher amounts of nitrogen, Ballweg stated. The lowest corn yield in 2015 was where barley had been the cover crop, probably because of the carbon to nitrogen ratio and tie-up of nitrogen.
At the varying rates of nitrogen applications, the plots where the clovers were grown produced higher corn yields in 2015 both where no cover crop and the barley were grown, Ballweg pointed out. He noted that the higher nitrogen application rates compensated for problems posed by the barley and stand problems with portions of the clover seeded in 2014.
To get a start in growing cover crops, Ballweg advised farmers to have a clear goal or goals such as reducing soil erosion, improving soil structure and water infiltration, obtaining nitrogen, enhancing crop rotations, and having patience for 5 to 10 years on gaining an increase in soil organic matter.
Understand what fits properly for the amount of growing time and 'avoid halfhearted attempts,' Ballweg stressed. Be aware of possible effects on follow-up crops in terms of terminating the cover crop, the carbon to nitrogen ratio in plant residue and any herbicide carry-over.
'Everybody has a learning phase,' he said. 'Be committed to learning about cover crops.'