Page 295 - Nutrient Management Planning Guide

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Chapter 8.3

Properly designed VFBs provide protection to surface water quality by removing sediment, organic matter, some nutrients and pesticides from runoff at the edge of the field before it enters the surface water bodies.

Other Benefits of VFBs:

They provide a habitat for wildlife. • They provide a source of forage or hay for livestock. • They become an area to turn equipment around at •

the end of field rows.

VFBs are most effective on sites with slight to moderate slopes where the runoff pattern from the field tends to be uniformly spread rather than concentrated in channels (i.e., sites prone to sheet erosion).

VFBs reduce nutrient export from fields that have received manure or fertilizer application through two main mechanisms:

Physical filtering. • Any sediment-bound nutrients are trapped in the strip rather than being carried into the adjacent water body. Larger-sized soil particles (i.e., sand and silt) and soil aggregates settle from the runoff within a relatively short distance into the filter. Fine particles such as clay may take a longer distance to settle out and, depending on runoff conditions, may not be deposited in the strip to any large extent. This filtering action would have little impact on reducing soluble nutrient concentrations in runoff.

Infiltration • . The velocity may be slowed to the point that water is allowed to penetrate into the soil allowing dissolved nutrients to be used by vegetation in the strip. With time this will result in the accumulation of nutrients within the VFB. For the VFB to function properly it must be regularly harvested to remove plant growth and accumulated nutrients. This mechanism does not work well in areas where soil conditions (i.e., compacted or frozen) during runoff impede infiltration.

Periodic monitoring of the nutrient status of the soil is required to prevent the VFB from becoming overloaded and turning into a nutrient source.

Establishing VFBs

When planning installation of a VFB, consider several site-specific characteristics:

soil properties • steepness of the slope • expected quantity and timing of runoff • shape and area of the field draining into the filter • management practices in use on the field that drains •

through the VFB.

The most important factors influencing the effectiveness of a VFB are:

The width of the VFB depends on its desired •

function and adjacent spaces. The width of a VFB to stabilize field edges that border steep ditches or steep banks will be smaller than the width necessary to effectively capture nutrients in runoff. For the VFB to filter runoff efficiently, runoff must •

pass through the strip in a shallow, uniform flow (i.e., sheet flow). This means they must be situated where runoff can be filtered before it concentrates in natural or manmade drainage channels which are influenced by the topography within the field. VFBs should be seeded perpendicular to the slope •

to create conditions that allow for shallow, uniform flow to enter the filter. Select suitable vegetation to ensure long-term •

effectiveness of the VFB. Suitable plants should have a dense top-growth, a fibrous root system, provide good, uniform soil cover and be suited to local soil and climatic conditions. If border vegetation is to be used for forage •

production, consider agronomic factors such as yield, feed quality and herbicide compatibility.

Heavy use of VFBs as field roadways should be avoided due to the risk of compaction and resulting loss of effectiveness as a filter.

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Other terms used interchangeably with VFB include grass barriers, riparian buffer strips and conservation buffers. This guide uses the term VFB to refer to all of these structures since they all perform the same basic function.

s i d e b a r