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Home > Protecting Our Lands & Waters > Clean Water Fund > On-Farm Projects > Perennial Veg Project

Cottonwood River Native Vegetation Water Quality


Principal Investigator: Adam Birr and Jeff Strock
Organization(s)
: Minnesota Corn Growers Association; University of Minnesota Southwest Research and Outreach Station
Sponsor
: MPCA 319 Funds
Award Amount
: $183,766
Start Date
: 4/26/2010 | End Date: 8/29/2014 

The final report is available through the Minnesota Water Research Digital Library

Overall Goal of the Project

Quantify the water quality and quantity characteristics of perennial vegetation on undisturbed soils and compare it to agricultural management practices commonly used in southwestern Minnesota.

Background and IntroductionNative vegetation at the Hick's Farm in Redwood County, Minnesota

Data quantifying the soil and water characteristics of perennial vegetation on undisturbed soils are very limited in Minnesota and in the Midwest as a whole. Typically studies have focused on such features as grass filter strips or have been conducted at a scale where water quality effects are confounded by multiple variables. This study will measure surface runoff characteristics of perennial vegetation on a hillslope of undisturbed soils using two different research designs.

Why is this important?

Many Total Maximum Daily Load (TMDL) implementation plans include the establishment of perennial vegetation, or the use of land set aside programs, to remediate pollution in the agricultural landscapes of southern Minnesota; however, the quantification of the water quality benefits of such programs as the Conservation Reserve Program (CRP) at the field scale is lacking. Best management practices designed to reduce sediment and nutrient export from agricultural watersheds will be more effective with a better understanding of the vegetation, soil, management and hydrologic controls that link spatially variable sediment and nutrient sources and sinks to transport processes at the field scale.

Location of the Study

The Hick’s Farm, located in Redwood County, includes a 160 acre field comprised entirely of perennial vegetation that has been part of the family farm since 1857. According to the family, the field was never planted with conventional row crops and no subsurface drainage has been installed. The field has not been grazed in over 20 years; however, the family does harvest the vegetation for forage approximately once per year. The perennial vegetation is composed primary of smooth bromegrass with a Kentucky bluegrass understory. Native forbs and grasses are also present; however, the native species make up a small amount of the overall plant diversity.

A hillslope located at the southern edge of the field was subdivided into three discrete drainage areas referred to as “watersheds” for the purposes of this study. Two of the watersheds are composed entirely of perennial vegetation (0.79 and 0.98 acres in size). A third watershed (1.7 acres in size) has approximately 0.67 acres utilized for long-term conventional row crop production that drains onto the perennial vegetation on the hillslope.

The Hick’s Farm is located within the Cottonwood River Watershed, a tributary of the Minnesota River. Soils in the study area consist of well drained loams and clay loams indicative of the region. The undisturbed soil at the site is classified as a Storden loam.

Analysis was completed to further examine how much of the greater Cottonwood River Watershed was composed of lands with similar slope that may serve as potential treatment areas to mitigate non-point source pollution between agricultural areas and floodplains. This analysis provided context for our results in terms of applying findings to a broader area. The majority of the land (88.2%) in the Cottonwood River Watershed has slopes under six percent; approximately nine percent of the land in the Cottonwood River Watershed was similar to the project site (slopes of 6 to 12%). The proper placement of perennial vegetation for water quality benefits within a watershed will be critical for maximizing the return of such programs.

Research Methods and Data Collection

Image showing the experimental design for this project

Results

Summary results are below. The complete project reports will be available on this page in early 2015.

  • Precipitation was extremely variable throughout the study period. Wet springs were followed by dry summers and falls. With this said, many months were above normal including the wettest May on record in 2012.

Monthly precipitation at the project site between January 2011 and August 2014

Paired Watershed Design

Note: NVe was converted to row crop production while the control watershed, NVw, remained as perennial vegetation on undisturbed soils.

Hydrology

  • No run-off was observed from perennial vegetation on undisturbed soils when the soils were non-frozen. Minimal run-off was observed during snowmelt in 2012 from the perennial vegetation on undisturbed soils.
  • Following conversion of perennial vegetation to cropland, four events occurred on the treatment watershed in 2013 resulting in 0.73 inches of run-off per acre.
  • Run-off was infrequent and of short duration: the average event on frozen soils lasted 5.4 hours; the average event on non-frozen soils (after NVe converted to cropland, only) was 42 minutes.

Sediment

  • Sediment losses were minimal from the perennial vegetation on undisturbed soils (run-off only occurred on frozen soils).
  • Sediment losses in 2013 and 2014 averaged 238 pounds/acre after conversion of perennial vegetation to cropland. Most of these losses occurred in a series of four events in June 2013.

Nitrogen

  • Nitrogen losses were minimal from the perennial vegetation on undisturbed soils (run-off only occurred on frozen soils).
  • The largest nitrogen losses were associated with the four non-frozen soil events at NVe post-treatment (after conversion to cropland).
  • Large nitrogen losses through surface run-off were not anticipated as most nitrogen losses occur through leaching or through artificial drainage (i.e. tile).

Phosphorus

  • The watersheds managed in perennial vegetation did have elevated TP concentrations; however, the export loads were low when combined with run-off volumes.
  • The watersheds managed in perennial vegetation also had a higher fraction of the TP in the DMRP form than from NVe after conversion to cropland.
  • The events with the largest TP export loads occurred at NVe in 2013 after conversion to cropland.

Soil Bulk Density

  • Soil bulk density increased from 1.25 to 1.40 g/cm3 in the first 10 cm depth following the conversion from perennial vegetation to cropland.
  • Soil bulk density in the lower 40-100 cm depth was similar for the recently converted cropland and an adjoining field that has been in row crop production for many decades.

Infiltration

  • Measurements of the infiltration at NVe pre-treatment were consistent with hydraulic conductivity of the adjoining perennial vegetation sites; measurements of the infiltration at NVe post-treatment were consistent with the hydraulic conductivity of the adjoining field that has been in row crop production for many decades.
  • There was a dramatic decrease in the amount of water that can infiltrate the soil after conversion to cropland from perennial vegetation.

Above and Below Watershed Design

Hydrology

  • The watershed with perennial vegetation captured more snow in the winter than the adjacent cropland and generally had a snowmelt of longer duration that had a higher run-off value for frozen soil conditions.
  • The watershed with a long history of row crop production had run-off more frequently during non-frozen soil conditions.
  • The watershed with the perennial vegetation effectively captured and infiltrated water leaving the watershed with a long history of row crop production.

Sediment

  • During frozen soil conditions, both watersheds had similar sediment concentrations in run-off.
  • The sediment yields were dramatically higher from the watershed with a long history of row crop production than the watershed with perennial vegetation.

Phosphorus

  • In both watersheds, a higher fraction of the total phosphorus was in the dissolved form for events over frozen soils.
  • The phosphorus yields below NVm was very low run-off volumes are included.

Nitrogen

  • Nitrogen yields were greater on both frozen and non-frozen soils from the watershed in row crop production compared to the watershed in perennial vegetation
  • Nitrogen losses from surface run-off were low as expected.

Soil Bulk Density

  • Soil bulk densities were much higher for the watershed with a long history of row crop production

Infiltration

  • Infiltration rates were similar between the two watersheds at the highest surface pressure potentials; however, the watershed with perennial vegetation had a higher rate as soils neared saturation.

MDA Contact

Bill VanRyswyk
Hydrologist
Bill.Vanryswyk@state.mn.us ~ 507-344-5260

Margaret Wagner
Supervisor, Clean Water Technical Assistance Unit
Margaret.Wagner@state.mn.us ~ 651-201-6488