Degree Type

Thesis

Date of Award

2015

Degree Name

Master of Science

Department

Natural Resource Ecology and Management

Major

Sustainable Agriculture

First Advisor

Richard C. Schultz

Abstract

Multispecies riparian buffers (MRBs) are a conservation practice that protects water quality and prevents soil erosion by improving soil quality including aggregate stability, particulate organic matter (POM), and water infiltration. USDA Conservation Reserve Program MRB contracts last 10-15 years; evidence shows MRB soil quality may improve within 3-7 years, but there is little data on how MRB soils perform after contracts typically expire.

Slaked soil aggregate stability was measured in a 20-21 year-old MRB in central Iowa at the surface (0-15 cm) and used to calculate the indices mean weight diameter (MWD), geometric mean diameter (GMD), and percent water-stable macroaggregates (%WSA). The MRB contained zones of switchgrass (Panicum virgatum L. ‘Cave-in-Rock’), hybrid poplar (Populus spp.), and cool-season grass; results were compared with an adjacent crop field, a formerly grazed pasture, and a natural riparian forest. Bulk density, total soil carbon, and POM were also measured.

A Cornell sprinkle infiltrometer was used to measure infiltration in a 10-year old tree and cool-season grass MRB, and in the switchgrass, cool-season grass and silver maple zones of the MRB used in the soil aggregate study. MRBs were compared with trafficked and non-trafficked crop interrows in a nearby crop field.

Perennial vegetation had greater MWD, GMD, %WSA, and total SOC compared to the crop field. Data collected in 1997 showed no significant differences in %WSA or MWD between switchgrass and crop field, but did between cool-season grasses and crop field. However, %WSA and MWD under switchgrass increased 45.8% and 120.5%, respectively, since 1997; under cool-season grasses %WSA and MWD increased 17.9% and 34.3%, respectively, since 1997, but decreased by 37.0% and 35.2% under row crops.

Sixty-minute cumulative infiltration did not significantly differ among MRBs, but was greater than trafficked crop interrows, and was best explained by rainfall rate, bulk density, and initial saturation. Percent rooted vegetation was not a significant factor explaining infiltration in MRBs.

Results suggest MRBs do continue to positively impact selected soil physical parameters. Switchgrass may take longer to improve soil quality parameters in MRBs. Soil quality improvements depend upon the edaphic factors and the amount of disturbance on site.

Copyright Owner

Leigh Ann Marie Long

Language

en

File Format

application/pdf

File Size

110 pages

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