Time to evaluate and maintain terraces
Aug 20, 2009 10:43 AM
After wheat harvest can be a good time to evaluate and perform maintenance on terraces, said DeAnn Presley, K-State Research and Extension environmental soil management specialist.
"Terraces must have adequate capacity, ridge height, and channel width to accomplish their purpose. Without adequate capacity to carry water, terraces will be overtopped by runoff in a heavy storm," Presley said.
Overtopping causes ero¬sion of the terrace ridge, terrace back slope, and lower terraces, and may result in severe gullies, she added.
Terraces need regular maintenance to function for a long life.
"Erosion by water, wind, and tillage wears the ridge down and deposits sediment in the channel. This decreases the effective ridge height, and channel capacity. Terrace maintenance restores capacity by removing sediment from the channel and rebuilding ridge height," Presley said.
Typically, more frequent maintenance is required for steep slopes or on highly erodible soils. Annual maintenance is necessary for intense tillage operations and heavy rainfall runoff. Less frequent maintenance is often adequate where there are high residue levels or where lower rainfall occurs and runoff intensity is low, the K-State specialist said.
Presley´s checklist for terrace maintenance activities:
1. Check for needed repairs. Check terraces and terrace outlets at least annually for needed repairs. The best time to check is after rains, when erosion, sedimentation, and unevenness in elevation are easiest to spot. Specific items to note are overtopping, low or narrow terrace ridges, water ponding in the channel, terrace outlets, erosion, and sediment clogging near waterway or pipe outlets.
2. Assess terrace shape. Assess what needs to be done before beginning maintenance. Compare the existing cross-section shape with the desired shape and size, and determine where soil should be removed and where it should be placed for the desired result. Back furrows are placed where more soil is needed, while dead furrows are located where soil needs to be removed. In this way, passes or sets of passes with the equipment are located to achieve the desired results.
3. Reshape the terrace if necessary. Terrace maintenance can be done with virtually any equipment that efficiently moves soil. Common tools include those that turn soil laterally (moldboard plow, disk plow, one-way, terracing blade or pull-type grader, 3-point ridging disk or terracing disk, etc.); those that convey or throw soil (belt terracer, scraper, whirlwind terracer, etc.); and those that push or drag soil (dozer blade, straight-wheeled blade, 3-point blade, etc.).
The main objective is to move soil from the channel to the ridge. Work done on the back slope or cut slope above the channel may help maintain or improve shape, but does little to add significant ridge height or channel capacity.
4. Consider making changes to increase terrace life. When silt bars and sediment deposits accumulate frequently in a terrace channel, excessive erosion is the cause. A change in tillage and cropping practices is needed to correct this. Conservation tillage and crop rotations that retain crop residue will reduce erosion substantially. This will reduce the frequency of terrace maintenance needs. Many no-till producers find terrace systems require little maintenance. Although runoff still occurs, there is little soil movement in a no-till system.
Terraces prevent gullies and are only part of an overall erosion control plan, Presley said.
"Conservation farming methods, especially crop residues, complement erosion control structures and have been shown to be both economically and environmentally sound," she said.
More information is available in the K-State publication C-709 "Terrace Maintenance," and through K-State Research and Extension county and district offices. Additional sources for technical information include U.S. Department of Agriculture Natural Resources Conservation Service and County Conservation District offices.
On-farm terrace maintenance demonstrations scheduled
Two on-farm terrace maintenance demonstrations sponsored by K-State Research and Extension have been scheduled for August and September.
The first event, sponsored by the Barton County Extension Office, will take place Aug. 27, at 5:30 p.m. For information, including directions to the field demonstration, producers and others should contact Rick Snell, Barton County Extension agent, at 620-793-1210 or rsnell@ksu.edu
The second event, sponsored by the River Valley Extension District, the Cloud County NRCS office and the Cloud County Conservation District, will take place Sept. 17, from 9 a.m. until noon. For more information, including directions to the field demonstration, producers should contact Todd Whitney, River Valley District Extension agent, at 785-243-8185 or twhitney@ksu.edu.
At both events, presentations will include:
* Terrace Maintenance, by Morgan Powell, K-State Emeritus Professor of Biological and Agricultural Engineering
* Maintaining Grass Waterways, by DeAnn Presley, K-State Research and Extension environmental soil management specialist
In addition, local contractors will demonstrate equipment, and a local producer will show the proper use of equipment in terrace maintenance.
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