Sediment Deposition Within a Watershed with Stiff-Stemmed Grass Hedges

Stiff-stemmed grass hedges planted in narrow rows within a field offer an opportunity for effective erosioncontrol at a reasonable cost. The objectives of this research were to evaluate the erosion control effectiveness ofgrass hedges in a typical field setting and to determine the amount of soil redistributed within a grass-hedged field.The research was conducted on a 6-ha watershed located in the deep loess hills region of western Iowa. Thewatershed was cropped primarily to continuous corn using conventional tillage practices. Collection of runoff andsediment yield data was initiated in 1975. In 1992, narrow rows of grass hedges were planted at 15.4-m intervalsto accommodate 16 rows of corn. A linear regression was developed between annual sediment yield and annualsurface runoff for the 1975 through 1991 period and used to estimate annual sediment yields for the 1992 through1999 period. Total estimated sediment yield for the 1992-1999 period was 209 Mg/ha compared to 75 Mg/ha thatwas actually measured, a reduction of 64%. Analyses of soil elevation data collected with a GPS RTK systemrevealed that 455 Mg/ha of soil was redistributed to cause soil elevation increases near the hedges and soil elevationdecreases further upslope. In areas of the watershed where rill and interrill erosion occurred, most of the soilredistributed was caused by tillage equipment moving soil downslope. The watershed has a well defined ephemeralgully network. There was considerable sediment deposition in areas where the hedges crossed the ephemeral gullies.Our results show the usefulness of narrow rows of stiff-stemmed grass hedges in reducing erosion and redistributingsoil between hedges in a natural landscape benching process.