Rain, rain go away, right on down the ditch and drain
July 19, 2021 By Haley Zinda, Wayne County Extension
It’s not a surprise to anyone that last week was a little wet. Okay, maybe a lot wet. Most folks I talked with reported no less than 2 inches of rain in a day of torrential downpours. For a 10-acre farm, that equates to 543,080 gallons of water! I won’t even mention the volume for larger tracts of land (hint: a 250-acre farm breaks 10 million gallons). Where is all that water going?
Unfortunately, most of that water won’t ever touch the roots of the crops those farms are growing. The water will end up rolling downhill into a drainage ditch, or if you are one of the unlucky ones, a self-made lake in the middle of the field.
This is where proper field drainage comes into play to prevent loss of crops, increase usable land, and increase plant root mass. Methods can include subsurface drainage (tile), surface ditches, or a combination of both. For those of you unfamiliar with tile, it’s not the ceramic floor tiles you may be thinking of – they are black corrugated plastic pipe ranging from 3” to 18” in diameter. Some may have perforations to allow water to seep in and be carried away. Tile is placed at the water table in the soil, or right above saturated soil. This of course depends on soil type, with some soils more readily saturated than others. For example, clay is more easily saturated and has low water permeability. Therefore, ideal tile depth will be around 3.0 to 3.5 feet deep. On the other hand, sandy loam will have a greater water permeability and tile can be place deeper in the ground, around 4.0 to 4.5 feet deep (NRCS 606).
Tile drainage efficiency can be manipulated by spacing between tile rows dependent upon soil type. Using our same clay example from earlier: for an “excellent” rating, tile is placed every 35 feet and can mitigate ½ inch of water per day. “Good” drainage clears about 3/8 inch of water per day with tile every 50 feet. “Fair” drainage is placed every 70 feet and will mitigate about ¼ inch of water per day. In comparison, tile in sandy loam would be placed every 150, 210, and 300 feet for “excellent,” “good,” and “fair” ratings, respectively (NRCS 606).
If you’re concerned that subsurface drainage will reduce the water available for crops, not to worry. Think of a tiled field as a giant porch flowerpot – the tile is simply the drain hole in the bottom to allow excess water to escape.
Agricultural ditches are a necessary part of most drainage systems. These provide channels for the water to reach streams, retention ponds, or road ditches. Most folks are familiar with the deep channel-type ditch with one depth. However, a two-stage ditch has, you guessed it, two depths. There is a step or bench between the top of the ditch and the deepest channel that acts as a flood plain in heavy rains. The Wayne County Soil and Water Conservation District supplies great resources and photos of two-stage ditches on their webpage if you haven’t yet checked them out.
Several benefits are associated with two-stage ditches. The first being a greater nutrient processing capacity than a channel ditch. The microbes living in the soil of the second stage decrease water nitrates through denitrification and increase nutrient uptake. Furthermore, the plants and roots of the second stage capture flowing sediment and prevent it from flowing further down the ditch. Lastly, the two-stage ditch design slows water flow compared to a channel-type ditch. Think of it this way: when you put your thumb over a flowing hose, the decreased opening increases the water pressure (channel ditch). Now, take your thumb away to allow a greater opening; the water pressure is dramatically reduced (two-stage ditch). Slower water flow along with plants to trap sediment will decrease the total amount of nutrients lost from runoff.
Water can be extremely damaging whether it is your basement or field that has flooded. Proper field drainage can increase plant growth by preventing water-logged soil and roots and may even help you farm that last area that usually ends up as a lake. Take some time to evaluate the feasibility and necessity of improving drainage and what it can mean for yields.
Photo courtesy of Illinois-Indiana Sea Grant
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