A Soil Remediation Project - Follow Up 13 Years Later

In 1991 OMAFRA staff worked with a Middlesex farmer in an attempt to restore the productivity to three eroded knolls in a field with the addition of soil and manure. The field was part of the OMAFRA/ University of Guelph Tillage 2000 project in the late 1980’s. Benchmark yields taken from different areas in the field identified the lower yielding eroded knolls. Soil was taken from the nearby depressions and moved to the knolls with the farm’s front end loader. Approximately 10 to 15 cm (4 – 6”) of soil was added to one-half of the three knolls. Manure was added to the top half of the knoll giving four treatments.

A year after applying the amendments a soil characterization was done on the most eroded knoll. This showed that where the soil was added, the topsoil layer (Ap) was thicker and the bulk density was lower than the no soil treatmeant. The soil structure was also greatly improved.

Yields were taken from the treatments on the most eroded knoll in the following years. The results can be found in Table 1.

The field has been in no-till since the remediation. The farmer has observed that the areas where the soil was added continue to perform better than where no soil was added. In the fall of 2004 one of the knolls was revisited to examine the soil properties 13 years after the remediation. The results can be found in Table 2.

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The top 6 inches where the soil was added generally has higher fertility and higher organic matter than where no soil was added. The lower 6 inches where the soil was added would be a similar soil to the area without additional soil and the soil test numbers reflect that.

The soil profiles were examined at the same time as the soil samples were taken. The depression area still has about 30 cm (12”) of topsoil and it is a dark brown colour, indicating a high organic matter level. The area where the soil was added shows two layers of topsoil, the added soil 15 cm (6”) and the original topsoil 12cm (5”). The added soil is a darker brown colour which agrees with the soil sample numbers. The area where no soil was added has about 15cm (6”) of topsoil and is a light brown colour. The profile from the nearby headland is a lighter colour still and has about 12cm (5”) of topsoil.

The remediation on this site was successful at improving the soil quality and yield in the long term. One of the limitations of this type of remediation is that there is usually more soil required to cover eroded areas than is available in the depressions. Generally, organic amendments are more feasible for soil improvement.

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