Fertilizers can leave a field by several different routes. The route most beneficial to the crop is, of course, uptake and removal by the crop. Unfortunately there are other, less beneficial, routes for fertilizer to leave a field including through soil erosion. Most nutrients applied to the soil erode off of the field when soil is moved by wind or water. That soil, and its attached nutrients, can be deposited in surface waters causing a number of water quality issues. This can be prevented through erosion management and conservation practices. It is a landowner’s job to work towards preventing erosion that leads to water quality problems.
There are several erosion management practices that utilize vegetation to trap soil and prevent it from reaching surface water. Vegetative conservation practices can be placed in a production field, around the perimeter, or away from the field near sensitive areas such as rivers and streams. Several common conservation techniques are discussed below. When planning any vegetative practice it is important that the plant species used is adapted to the geography and specific soil conditions and not be considered invasive.
One of the most common in-field vegetative practices is a grassed waterway. A grassed waterway is a shaped or graded channel planted to suitable vegetation that directs water to a suitable outlet. The ideal characteristics for a grass species in a grassed waterway is one that has stiff, upright stems that can withstand heavy water flow and sedimentation. A dense stand of stiff stemmed grasses will slow down water flow as it enters the waterway. When water flow slows down the sediment in that water will settle out of the water and remain trapped by the grass. The clean water will then travel down the waterway to the outlet.
Grass species common to the Midwest and eastern United States include, but are not limited to, cool season grasses such as bluegrass, ryegrass, and fescues. Species common to the southern United States include, but are not limited to, warm season grasses such as Bermuda grass and sideoats grama.
There are several conservation practices that can be installed around a field or near environmentally sensitive areas. Field borders and filter strips are plantings of permanent vegetation using stiff stemmed upright grasses, legumes, and forbs to trap soil particles suspended in wind or water. A combination of cool season and warm season grasses can be used for this purpose. Cool season grasses such as wildrye species, junegrass, wheatgrass species and bottlebrush are considered native to the United States. Those grasses will have fast vegetative growth in the spring and early summer, and again in the fall. Prairie grasses such as big bluestem, little bluestem, Indiangrass, and switchgrass are common warm season grasses that can be used, and their fast growth period is from early summer until early fall. Warm season grasses will often have thicker stems than cool season grasses and the senesced stems will usually provide a filtering effect throughout the early spring until cool season grasses grow enough to become effective as filters.
If the landowner or manager wants to provide additional wildlife habitat there are many choices of forbs and legumes that can be added to the planting. Forage legumes such as clovers, birdsfoot trefoil, and alfalfa provide diversity in the planting and fix nitrogen from the atmosphere. Many forb and wildflower species can be added to supply habitat for pollinator insects. Wildflower planting should have enough species to provide flowering throughout the growing season so that pollinator insects will have a food source during the entire season. Not all wildflowers are attractive to pollinator insects. Refer to local recommendations for species selection.
Grasses, legumes, and forbs are not the only plants that can be part of conservation practices that prevent sediment and nutrient runoff from a field. A riparian forest buffer where trees and shrubs planted adjacent to streams and rivers can also serve an important role in protecting surface waters. The trees and shrubs planted against a river or stream will hold soil in place with their root systems and their leaves reduce the impact of raindrops on the soil surface. They can also be used to help stabilize stream banks, provide additional wildlife habitat, and improve overall water quality of the stream or river. Short tree and shrub species may include alders, dogwoods, willows, sumac and elderberry. Tall trees may include maples, birch, oaks, and cypress species. Riparian forest buffers are often installed in conjunction with filter strips.
Once a conservation practice is planted and established it is important to perform maintenance on them at various times. Maintenance tasks may include mowing, spraying, burning or pruning. Performing timely maintenance will improve the effectiveness of the practice and extend the life of the planting.
There are many resources available to help plan, establish, and maintain these conservation practices. The USDA Natural Resources Conservation Service has information on design and species selection that are appropriate for each local area. There may also be State and local resources in an area to help with this planning.