Soil Conservation and Pest Management Impacts of Grass Hedges

Soil Conservation and Pest Management Impacts of Grass Hedges

Summary

Objectives
1) Evaluate erosion-control effectiveness of grass hedge field plantings.
2) Increase understanding of response of arthropods to hedges in cotton production systems.
3) Increase information delivery of grass hedge technology to limited-resource farmers.
4) Evaluate farmer responses to farming with grass hedges and share experiences with others.
5) Incorporate new knowledge into an improved USDA-NRCS standard and specification.
6) Develop a computer program to predict the long-term impact of benching between hedges on runoff, soil
erosion, and productivity.

Erosion control effectiveness was evaluated by observing and surveying fields where hedges had been in place for up to 9 years. The amount of soil moved by tillage between hedges was quantified experimentally.

Significant bench terrace formation was observed due to soil translocation from erosion and tillage processes. Current erosion prediction models, including WEPP and RUSLE, do not account for slope variation over time. We developed a computer model that does this and found reductions in erosion by 75% as a result of slope modification predicted from farming between hedges for 12 years.

Insects were monitored with pheromone traps and sweep nets in grass hedges and in crops adjacent to hedges. Winter temperature regime in hedges and nearby habitats was also monitored to determine their value as overwintering habitat for insects. Sampling included extensive trapping for boll weevil (Anthonomous grandis) and various species of ants and sampling for tarnished plant bug (Lygus lineolaris) and beneficial natural enemies. Very few insects were associated with hedges that were free of broad leaf weeds. Numbers of plant bugs increased significantly with appearance of preferred host plants of plant bug such as pigweed, mare's tail, daisy fleabane or curly doc. In these cases there were minor infestations of tarnished plant bug in hedge weeds. Significantly higher numbers of ants (beneficial predators) were associated with the hedges and in rows closest to the hedges than in areas of the field not influenced by hedges. Pheromone trap catches indicated that the hedges provide better overwintering habitat for boll weevils compared to mowed grass/mixed forb strips located along roadways, but habitat was not as favorable for overwintering as deciduous field boarders.

Soybean growth, soil water content, and crop yield were measured in transects oriented perpendicular to grass hedges of unclipped ‘Alamo' switchgrass, clipped Alamo, or two shorter switchgrass accessions.
Unclipped Alamo grew to 8 ft in height, had a canopy spread of 12.5 ft, and reduced soybean yield in the first adjacent row. Clipped Alamo and the shorter accessions did not reduce soybean yield. Soil water contents were higher under the row adjacent to unclipped Alamo, indicating that yield reduction was due to shading.

Farmers, conservationists, and project scientists interviewed at the initiation of this project generally agreed that grass hedges would be an effective deterrent to erosion. However, there was concern about the possible side effects such as harboring harmful insects or the introduction of unwanted weed seeds. Return interviews to determine alterations in attitudes based on experiences in the projcet are planned for year 2000.

Grass hedges, called Vegetative Barriers by the USDA-NRCS, was selected to be one of ten types of conservation buffers included by NRCS in their CORE4 training program. Training materials were published on CD-ROM; the second edition of 5,500 copies is currently in press. In 1999 NRCS formed a committee, which included Seth Dabney, to draft a new national practice standard for Vegetative Barriers. Draft results of that committee's work have been posted for comment on an internal NRCS web site. Proceedings of a recent grass hedge workshop held in Beltsville, MD, are available at:
http://rhizo.ars.usda.gov/grasshedges/ .