Author: Raylene Nickel
Cow-calf producer and no-till farmer Lance Gartner, Glen Ullin, North Dakota, grows full-season cover crops to build soil health and to provide early-winter grazing for cows.
Soil organic matter has increased as a result of the multispecies cover crops and the fertility contributed by cattle manure and urine. “Before I started growing cover crops seven years ago, soil tests showed my no-till soils had 2.3% to 2.9% organic matter,” says Gartner. “In recent years, my soils have tested 3.7% to 4.25% organic matter.”
The building of soil organic matter results in a reduced need for applying nitrogen (N) to wheat and corn. Gartner has reduced commercial N use for these crops by 60%, and sometimes he eliminates fertilizer applications altogether.
The yardstick guiding Gartner’s N-application rate is his estimate of N mineralizing from the organic matter. “The unavailable nitrogen doesn’t show up on soil tests, and what mineralizes is not immediately available to plants,” he says. “It becomes available to the crop slowly throughout the growing season.
“I allocate about 1,000 pounds per acre of unavailable N for each percent of organic matter,” he says. “I then figure 1% of this 1,000 pounds of unavailable N will mineralize. This yields 10 pounds of available N. When multiplied times 4% of organic matter, the result is a nitrogen credit of 40 pounds of available N per acre.”