Removing terraces from no-till cropland may sound like a good idea, since it would make field operations much easier in many instances.
No-till management can result in increased water infiltration capacity thereby reducing the volume of water moving down slope. Maintenance of surface residue reduces sheet and rill erosion, which further reduces the perceived need for terraces.
But growers must understand the benefits that terraces provide. As water moves down slope it gains volume, as well as speed. Terraces are generally designed to slow water down and divert it to an outlet. The maximum water volume and its speed are reduced because the terraces effectively shorten the slope length.
This reduces sheet and rill erosion and, perhaps more importantly in a no-till situation, prevents gully erosion. Regardless of residue, if sufficient water moves down slope and is channelized, gullies can form regardless of residue. In contrast, sheet and rill erosion are very effectively controlled by maintaining residue.
Most terraces were designed to handle a 10-year rainfall event. Therefore, larger events have the potential to overtop terraces even if they are properly maintained.
The benefits of no-till, with respect to decreased runoff volume, will make terraces more effective at protecting the soil from large events. But if no terraces were in place during a large event, water moving down slope could gain sufficient volume and speed to wash residue and then soil down slope.
This could potentially cause severe damage regardless of the amount of residue present on the field. In short, terraces provide protection from large rainfall events.
Another concern with the removal of terraces is that they provide insurance against the loss of sufficient surface residue.
Surface residue accumulation and maintenance is an important component of a no-till system for a number of reasons. However, it can be a struggle sometimes.
The inclusion of a low-residue crop in rotation such as cotton, grazing, or simply a drought resulting in low-residue production can all result in a field having limited residue at some point in time. Intact terraces will prevent a low residue situation from becoming a catastrophic erosion event.
Lastly, removal of terraces will require a lot of earth to be moved, which would in itself be expensive. Replacing them in the event that they are later required would be equally or more expensive.
Terraces are protective infrastructure that should be maintained regardless of tillage, because they provide a layer of protection from large rainfall events. We may not need them very often, but the next 20-year rainstorm would certainly make us realize why they are important if we decided to remove them.