A recently completed five-year study of conservation tillage practices in the 4.9 million acre Western Lake Erie Basin watershed reveals that most fields in the watersheds are either tilled conventionally or stirred with mulch tillage at least once every three to five years. Crop rotations including corn were the reason fields used conventional tillage periodically. Corn in a crop rotation was planted using conventional methods 80% of the time.
"There are varying degrees of conservation tillage," explains Steve Davis, a watershed specialist contractor working for the Natural Resources Conservation Service. The amount of crop residue cover on the field at planting and the degree of soil stirring determines the type of conservation tillage. No-till planting, in which the crop is planted directly into the prior crop residue with a minimum of disturbance, leaves the most residue. "There is a lot of no-till planting in the watershed," Davis says, "but the percentage of long-term continuous no-till fields is still small."
These findings are significant when considering the role conservation tillage plays in delivering phosphorous runoff to waterways in the Lake Erie drainage basin. Increasing levels of dissolved (soluble) phosphorous have been identified as a major factor in recent algal blooms. Some thinking points to no-till as a main culprit, alleging the phosphorous applied to no-till fields stays in the top layers of the soil which may run off easily.
Davis refutes the claim that no-till alone is the major cause of the increase in phosphorous based on the findings of the survey. He points out that while phosphorous does run off from no-till fields, especially if rain occurs right after application, the same holds true if phosphorous is applied to the surface on conventionally tilled fields. Davis also points out that the conventional tillage occurring at some time in most crop rotations in the watershed incorporates the phosphorous deeper into soil layers as compared to continuous no-till systems.
Several factors working in concert are a more likely explanation for increasing levels of dissolved phosphorous runoff. Davis lists changes such as the methods and timing of fertilizer application, more broadcast surface application versus row fertilizer, application of fertilizer in winter months or on frozen ground, increased soil compaction from larger equipment, and a trend towards applying two years worth of fertilizer on a corn crop as other contributors to the phosphorous increase.
The use of conservation tillage is critical to controlling sedimentation of waterways and Lake Erie. Davis believes going backwards on no-till is not the answer. He suggests the uncertainty surrounding the increasing dissolved phosphorous runoff levels points out the need for substantial new and additional research to determine the exact forces driving the changes in phosphorous levels. Davis also noted that according to water monitoring data, while dissolved phosphorous has increased in runoff, both particulate phosphorous and sediment in runoff has declined as a result of the conservation practices that have been applied in the Lake Erie watershed.
In the meantime, farmers in these watersheds aren't standing still. Using the technical and financial assistance from the NRCS and its Environmental Quality Incentives Program, over $4.9 million have been applied to 462,262 acres since 1996 for nutrient management systems in the watershed that control phosphorous runoff. NRCS has given priority to incentives for nutrient management systems within the Great Lakes Restoration Initiative area. These systems use a variety of conservation practices, including no-till, cover crops, precision nutrient application, and controlled traffic, working together to reduce non-point runoff.
"I agree we certainly need to drastically reduce dissolved phosphorous runoff in the watershed," Davis said, "but no-till is an important tool in a farmer's conservation toolbox. In my crystal ball, I don't see farmers going back to the days of fencerow-to-fencerow moldboard plowing and all the problems that caused. Fuel prices won't allow that, costs of cleaning drainage ditches and dredging harbors won't allow that, and certainly a public that values clean water won't. Let's put our energies into more research to find nutrient management Best Management Practices that work with no-till to reduce the soluble portion of phosphorous in our runoff."
For more information on the results of the Conservation Tillage Survey, visit www.oh.nrcs.usda.gov/technical.