The use of continuous conservation tillage is encouraged because of its contribution to soil quality and environmental protection. Many studies report the benefits of increased soil organic matter and related soil quality gains. Farmers who adopt a system of continuous no-tillage generally find that, compared to conventional tillage, the firmness of these “no-till fields” facilitates the equipment traffic they need for crop production. Growers understandably assume that soil conditions in the prime root zone are near ideal for crop initiation and growth. However, poor crop growth and yield have been observed in some areas of fields under long-term no-till culture, especially following early-season periods of cool, wet weather.
We investigated the relationship between soil bulk density and the soil carbon/total soil N contents at depths of 0-2 and 2-5 inches, taking all samples as undisturbed 3-inch diameter cores. We sampled differing soils within a field-scale, six-year tillage experiment, and later, a larger study of farm fields with varying soil properties across North Carolina. All sampled farm fields had six or more years of no-till crop culture.
The conservation tillage systems studied demonstrated substantial amounts of increased carbon sequestration within the surface five inches of soil, compared to conventional tillage. The additional carbon sequestration and nitrogen captured through conservation tillage systems will be reported.
We found that the surface two inches of soil under conservation tillage generally had maintained suitable density for root activities. At 2-5 inches, however, soil density often approached 1.6 g cm -3. Given the textures involved, this density likely affected root growth unfavorably, especially under non-ideal, wet/cool or dry/hard conditions during crop establishment.
We found strong, inverse correlations between soil carbon and soil density, and concluded that the dense soil zones below 2 inches occurred because of inadequate carbon content to protect against high density. This low-carbon/high-density problem was related to soil texture, occurring in soils having strong sand influences versus those of more silt and/or clay content. This is similar to prior findings about problems of tillage pans, especially in soils with more sandy surface textures common in the Southeastern Coastal Plain. Achieving full yield potential and grower satisfaction with long-term no-till grain crop culture will sometimes require some soil loosening within the row zone (strip tillage). Studies of alternative cover crop or rotation strategies aimed at deeper deposition of soil carbon should also be explored.From our extensive paired sampling of farm fields we developed useful regression equations allowing prediction of the necessary level of soil C associated with favorable soil density under continuous no-tillage culture. This information could be used as a timely educational aide for growers and others, as well as in monitoring and demonstrating field-level progress toward agronomic success and soil quality.
George Naderman - Dr. George Naderman is a retired Extension Soil Specialist for North Carolina State University in Raleigh. For decades Dr. Naderman’s Extension Program emphasized the use of applied research and demonstration studies involving various tillage practices in the production of most of the major field crops of North Carolina. Those studies were conducted under practical farm conditions with most of them including, or even emphasizing, the successful use of conservation tillage. George has been a supporter of many programs of the Soil and Water Conservation Districts. One of these is the NC Resource Conservation Workshop, introducing high school students to conservation issues and career opportunities. He is a long-term member and Fellow of the Soil and Water Conservation Society and has served as President of the Hugh Hammond Bennett Chapter in North Carolina.