Grassed waterways play an important role in improving water quality. Prevention of gully erosion is the primary contribution, but grassed waterways also intercept pollutants leaving the field. Grassed waterways are designed, however, for the safe and rapid transport of water, not for the shallow sheet flow necessary to effectively intercept pollutants. Because waterways are a flow-way for excess runoff, nutrient and pesticide applications within the boundaries of grassed waterways must be carefully managed to avoid movement of pollutants directly to surface water. Although many grassed waterways have been replaced with underground tile outlet terraces, the amount and intensity of rainfall for 2019 is a reminder that grass waterways are an extremely valuable part of a whole-farm and watershed-wide conservation system.
Waterways are only one component of a conservation system that includes terraces, conservation tillage, residue management, good crop rotation or use of cover crops, and nutrient and pest management. A well-designed and maintained soil conservation system helps sustain productivity while providing clean water to the watershed.
Fertilization and liming of waterways
The primary purpose of a good fertilization program is to ensure that waterway grasses grow vigorously and maintain a dense, tough, non-erodible sod. Soil testing is an integral part of establishing waterways. Soils should be limed and fertilized according to soil test recommendations. In areas where the subsoil is exposed during construction, a onetime application of manure is a good way to build organic matter and provide nutrients. Any amendments should be well incorporated before seeding. Once established, waterways require annual maintenance. For stand maintenance of cool season grasses, an annual application of 30 to 40 pounds of nitrogen (N) per acre is recommended. Nitrogen should be applied between late November and mid-March. Higher N rates will be necessary when managed for hay or seed production.
If seed production is desired, N fertilizer should be applied before soil freezing in November or December. On soils low in phosphorus (P) or potassium (K), an application of these nutrients, according to soil test recommendations, should be included. Soil tests should be conducted every 3 to 4 years on established waterways to monitor soil pH, P, and K levels. Needed P and K can be applied at the same time as N fertilizer. If lime is needed on established waterways, apply no more than 2,000 pounds ECC/a (effective calcium carbonate per acre).
Routine inspections and maintenance
Waterways should be inspected at least annually and, if possible, after each heavy rain. When problems develop, perform needed maintenance promptly to prevent additional, costly damage to the waterway. Abuse and neglect are the most common causes of waterway failure. Common maintenance problems include weeds and brush, eroded spots, sediment deposits, bare spots, and insufficient grass stands. Maintenance activities may be needed more frequently when the waterway handles a large volume of water or is on a steep slope.
A vigorous grass stand, maintained with routine mowing and a well-balanced fertilization program, will help control with weeds and brush. Weeds and brush also can be controlled by cutting, grazing, or herbicide use. The current issue of the K-State Research and Extension publication Chemical Weed Control for Field Crops, Pastures, Rangeland, and Non-cropland has recommendations on herbicide use. See: http://www.ksre.ksu.edu/bookstore/pubs/SRP1099.pdf
Avoid herbicides with a high potential for runoff. Herbicides used on adjacent cropland may harm grass stands when transported in runoff water or attached to sediment. Damage also can occur when the sprayer is not turned off while crossing waterways.
Waterway maintenance includes mowing. Timely mowing provides an even growth of grass in the spring and minimizes sediment buildup where terraces connect to the waterway. Frequent mowing or shredding can prevent smothering without removing the clippings. Some grasses, such as fescue, tend to become clumpy when mowed infrequently. Grass clumps can concentrate water flow, causing erosion and creating channels.
Gully formation is the most serious problem in a waterway. It is usually caused by poor management, sediment deposits, using the waterway as a roadway or livestock trail, or by an unstable outlet. Eroded spots should be filled promptly, compacted, and reseeded or sodded. Slight overfilling allows settling. Reseeding perennial grasses with annuals such as wheat, oats, rye, or annual ryegrass will help ensure that good cover is quickly re-established. During grass establishment, divert runoff by use of silt fences or by low elevation earth berms. For unstable outlets, grade stabilization structures may be necessary. Minimize machine travel within waterways, especially when the soil is wet or soft. Try to limit traffic within the waterway, using the sides, or berms to drive.
Sediment accumulation results from insufficient water velocity and is most common where water from terraces discharges into the waterway. Sediment deposits should be removed promptly, because they tend to increase with subsequent runoff events, eventually blocking the waterway. In severe cases, reshaping and reseeding the waterway may be the best option for restoring waterway capacity. Reseeding grass in a waterway may be necessary in cases of initial establishment problems, smothering from lodged growth or improper mowing, sedimentation, weed and brush competition or herbicide damage. For limited sized areas, reseeding can be enhanced by mulching and slight overfilling of reseeded areas. Before reseeding, correct nutrient or soil pH deficiencies and perform any other maintenance. Sometimes temporary dikes constructed at terrace outlets are necessary to protect reseeded areas from runoff.
Managing for production
Waterways not only serve to route excess runoff safely to streams, but they also can be a source of income. Grassed waterways frequently lie within productive soils and by design receive a greater proportion of precipitation than the fields they drain. Waterways can provide protein-rich forage for grazing or haying, or they can be managed for seed production. A good fertility program can increase production of forage and/or seed. Well-fertilized waterways can provide high protein forage that helps balance the ration when crop residue is grazed in the fall.
Annual haying is an excellent management practice. With adequate fertility and timely cutting, waterways can provide high-quality forage. Cutting height should not be less than 3 to 4 inches. To maximize quality and quantity, fescue hay should be made in the early boot stage, and brome should be hayed in full bloom.
For specific management recommendations, consult K-State Research and Extension publications:
Smooth Brome Production and Utilization, C-402
Soil Test Interpretations and Fertilizer Recommendations, MF-2586
Keeping the waterway clear prevents the slowing of water and reduces the sediment accumulation. Any harvested hay should be quickly removed to prevent smothering of vegetation. However, harvest only when the waterway is firm enough to prevent wheel ruts. If the soil is too wet for traffic, postpone harvest to prevent damage to the waterway. This may reduce hay quality, but protecting the waterway structure is more important.
Waterways also can provide excellent seed production. After the seed is harvested, the remaining grasses should be hayed or mowed and clippings removed.
Grazing of waterways may be possible, but grazing should be strictly controlled. Enough plant growth must be left to maintain a healthy, vigorous sod. Never permit overgrazing, and do not graze when the soil is too wet, during initial establishment, or during reseeding of problem areas.
A waterway also can be managed for optimum wildlife habitat by selecting specific grass species and mowing practices. Mowing should be done at a time that does not interfere with the nesting, hatching, or rearing of wildlife. Contact your local Natural Resources Conservation Service or Kansas Department of Wildlife, Parks, and Tourism office for additional information.
Note: This article is adapted from Maintaining Grass Waterways, K-State publication MF-1064 at: http://www.ksre.ksu.edu/bookstore/pubs/MF1064.pdf
DeAnn Presley, Soil Management Specialist