Soil Hydraulic Property Impacts of Incorporating Prairie Vegetation within a Row Crop Production Area

Lockett, Delise
Major Professor
Matthew J Helmers
Chris R Rehmann
Committee Member
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Agricultural and Biosystems Engineering

Vegetative filter strips (VFS) and buffers have long been recognized as a viable option for managing land and water quality in regions where erosion is prevalent. Many studies have been conducted to evaluate the extent to which introduction of VFS reduces runoff, limits soil loss, and influences soil properties. These studies have compared the use of various vegetation as well as various in-field management styles such as conventional tillage, reduced tillage, and no tillage. However, there are still many questions as to the overall effectiveness of VFS dependent upon size, location, vegetation, existing soil characteristics, and age of the strips. Though many studies have been conducted there is still a need for investigating the use of alternative vegetation forms such as native prairie vegetation in filter strips. This research explores the use of native prairie vegetation within the filter strips which have been strategically located within an agricultural field managed under a no tillage corn-soybean rotation. The first objective was to determine if incorporation of native prairie vegetation within an agriculture system will have an effect on soil physical properties specifically hydraulic conductivity and soil bulk density. The second objective was to determine if slope position also had an effect on soil physical properties.

Small experimental watersheds at the Neal Smith National Wildlife Refuge (NSNWR) in Jasper County, Iowa were used. In the watersheds soil hydraulic properties under the cropped area were directly compared to the soil properties within the VFS to determine if the soil properties in the filter strips had changed significantly. Unsaturated and field saturated hydraulic conductivity were obtained in situ using tension infiltrometers near the same locations where soil cores were extracted for lab analysis of saturated hydraulic conductivity and bulk density.

Changes in soil properties varied greatly among the three watersheds and the two experimental years. Most results lacked significant differences in treatment and position. Results showed that VFS generally had a greater overall number of pores than row crop. In situ analysis showed conductivity of row crop to be greater, though not significant, than VFS and restored prairie at field saturation, K(0) and most other tensions. However laboratory determination of saturated hydraulic conductivity, Ksat was the opposite and showed greater Ksat in the VFS followed by the restored prairie with the lowest measured Ksat in the row crop. Position results varied greatly depending on analysis and year though only the up slope position in 2011 had significantly greater hydraulic conductivity than the foot slope position.

The results indicate that land cover and land position had little effect on soil hydraulic properties. Some of the watersheds showed a response from implementation of VFS treatments in a short amount of time while others may require more time. There is some indication that large amounts of prairie vegetation may potentially produce temporal negative impacts on some soil processes such as infiltration rate, which could be due to roots occupying vital pore space. However, temporal effects were not a part of this study; this is an aspect that warrants further investigation. In summary, while there is some evidence of improved soil hydraulic properties in VFS compared to row crop generally the results were not statistically significant. Thus, the study should be repeated again after more time has passed to determine if significant differences have developed and more conclusive results obtained.