Wikipedia
A buffer strip is an area of land maintained in permanent vegetation that helps to control air, soil, and water quality, along with other environmental problems, dealing primarily on land that is used in agriculture. Buffer strips trap sediment, and enhance filtration of nutrients and pesticides by slowing down runoff that could enter the local surface waters. The root systems of the planted vegetation in these buffers hold soil particles together which alleviate the soil of wind erosion and stabilize stream banks providing protection against substantial erosion and landslides. Farmers can also use buffer strips to square up existing crop fields to provide safety for equipment while also farming more efficiently.
Buffer strips can have several different configurations of vegetation found on them varying from simply grass to combinations of grass, trees, and shrubs. Areas with diverse vegetation provide more protection from nutrient and pesticide flow and at the same time provide better biodiversity amongst plants and animals.
Many country, state, and local governments provide financial incentives for conservation programs such as buffer strips because they help stabilize the environment even when the land is being used. Buffer strips not only stabilize the land but can also provide a visual demonstration that land is under stewardship.