ABSTRACT:
Effectiveness of filter strips may change over a period of years because key soil and vegetation conditions change after conversion of cultivated farmland to permanent vegetation. The main objectives of this study were to: 1) determine if effectiveness of a filter strip changes over years since establishment, and 2) determine if temporal change depends on vegetation type. Four vegetation treatments were replicated five times in 3 × 7.5 m (10 × 25 ft) plots. Plots containing all-grass (New Grass) and grass with trees and shrubs (New Forest) were established in spring of 1995 among otherwise similar plots that contained either grass since ca. 1970 (Old Grass) or were re-cultivated and re-planted annually with grain sorghum (Crop). Once each summer, in 1995, 1996, 1997, 2003, and 2004, identically prepared solutions containing sediment, nitrogen (N) and phosphorus (P) fertilizer, and bromide tracer were applied to the upper end of each plot during a simulated rainfall event of 2.5 cm (1 in) in 30 minutes, and the load and concentration of runoff components were measured in outflow from the plots. Retention of solution components and reduction of their concentrations by the New Grass and New Forest plots improved from effectiveness similar or less than the Crop plots to effectiveness similar to the Old Grass plots within three growing seasons. Improvement coincided with the development of denser vegetative ground cover and a slower rate of runoff flow through the plots. Change in infiltration accounted for most of the improvement in overall effectiveness. There was no evidence of divergence in the performance of New Grass and New Forest plots. We conclude that filter strip performance improves over a period of years since establishment. Most of the change occurs within three growing seasons after establishment. Infiltration characteristics account for most of that change. Grass and forest vegetation are equally effective as filter strips for at least 10 growing seasons after establishment.
Footnotes
Michael G. Dosskey is a research ecologist at the U.S. Department of Agriculture Forest Service's National Agroforestry Center in Lincoln, Nebraska. Kyle D. Hoagland and James R. Brandle are professors in the School of Natural Resource at the University of Nebraska in Lincoln, Nebraska.
- Copyright 2007 by the Soil and Water Conservation Society