Why do they do that? – Terraces and Tile Lines

Much of Iowa seems flat, but as we’ve previously discussed there is actually a lot of variety to the Iowa landscape. In addition to this, many Iowa farmers dabble in terracing – creating terraces on the slope of a hill. But why do they do that?

Maybe you’ve never even noticed it, but look closely at Iowa fields – especially in the southern half of the state – and you will see terraces on many hillsides.

One thing that Iowa farmers struggle with is soil loss and erosion from water running across the field. When water after a rainstorm flows across the field it can pick up soil particles and carry those particles downstream. Loosing that soil off the field might make the field less fertile. The steeper the slope or grade of the land (like a hillside) the faster the water will move. The faster the water moves, the more soil it might pick up and carry away with it.

Avoca Terraces

Terraces placed on the slope protect the soil from erosion. Photo courtesy of USDA-NRCS, Iowa.

So farmers need to try and slow down the movement of water. Hence, terraces. Terraces are man-made earthen structures that intercept runoff on slopes. They change long slopes into a series of shorter slopes. At each level of the terrace, water has a chance to slow down and the soil has a chance to settle out which keeps it on the field. The result is that cleaner water leaves the field and not as much erosion occurs.

Farmers mound up soil on the hillside creating a somewhat level area with a short steep backslope down to the next level. The top, flat area can still be farmed with crops. The short steep backslopes are seeded with perennial grasses. The roots of these perennial grasses help hold the slope in place.

Sometimes terraces can also include a tile line and drain. In some cases and if there is considerable water build up, farmers can install a tile line and drain. This will allow the soil to settle out and the water to be siphoned off into an underground pipe. This allows the water to run through the pipe down the slope without collecting any soil. The water is discharged at the end of the pipe. This also reduces soil compaction and and enables good root development.

In Iowa, terraces are a fairly common practice. In fact hundreds of miles of terraces help cut soil loss. In one watershed management area terraces reduce soil loss by as much as 13 tons! New terraces might be installed in the fall of the year after growing crops have been harvested or in the spring of the year before crops are planted. In addition to reducing soil erosion, terraces can help retain moisture for growing crops and water conservation purposes. Terraces can even help create nesting habitat in the grassy back slopes that are largely untouched.

-Will

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