Discovery Farms programs in Minnesota and Wisconsin have collected edge-of-field water quality information from 24 farms and 45 fields starting in 2002. A total of 112 site years of surface runoff data and 47 site years of tile flow have been collected at the various locations. This large dataset allows for review and analysis of important water quality topics. This blog examines the factors that impact soil loss in tile systems.
Soil loss is mainly transported by surface runoff, however, there are a few tile sites with higher losses. For surface runoff, the median annual soil loss is 109 lb/ac with a typical range from 33 to 331 lb/ac. This median equates to about 3 five gallon pails full of soil from an area the size of a football field. For tile flow, the median annual soil loss is 18 lb/ac with a typical range from 7 to 64 lb/ac. There have only been three tile monitoring sites that have had greater than 150 lb/ac soil loss in a year.
Tile monitoring sites with higher concentrations of sediment were older cement or clay tile systems and some had surface intakes or tile collapses. Of 14 sites monitored, the 7 with corrugated plastic tile had almost no soil loss compared to the 7 with cement or clay tile lines which saw a range of soil loss.
Updating and maintaining tile drainage systems will decrease the amount of soil loss. Here are three keys to reducing soil loss in tile systems.
- Modernize old cement or clay tile systems with corrugated plastic pipe. Older cement or clay tiles were not perforated like the modern corrugated plastic tile that is common today. These older cement or clay systems relied on short lengths of pipe which were butted up against each other with most of the water entering the pipe through the gap where the short lengths of pipe touch. The gap at the connection of the cement or clay pipes is larger than the perforations in modern corrugated plastic tile and allows more soil particles to pass through.
- Update tile systems to remove the need for surface intakes where possible. Surface intakes are a source of soil loss because they are direct connections to surface flow and allow more soil into the tile system.
- Prevent tile collapses. Tile collapses result from excessively high flow velocity or pressure inside the tile, causing it to crack or burst. Collapses will often create a direct conduit to the soil surface when the surrounding material is drawn into the tile and transported downstream. They range in size from a few inches to several feet and can be hard to find. Tile collapses are caused by a failure of tiles from degradation over time, inadequate venting, expansion of tile system without adequately resizing main, blockages of outlets, improper joint connections, contact with tillage equipment, or animal burrows.