Microclover - Tall Fescue Lawns in the Mid-Atlantic Region

Amending Soil with Compost to Reduce Stormwater Runoff and Lawn Fertilizer Use

Compost to Reduce Runoff and Lawn Fertilizer Use

Soil Restoration of New Residential Lawn Areas: A House Divided

Mark Carroll, Ph.D., University of Maryland

Recent emphasis on the use of stormwater management practices that incrementally reduce runoff has emphasized the need to retain previous areas in new developments and to restore the hydrologic function of the soil in these areas when it is compromised by construction activity. Soil compaction, while necessary to stabilize the foundation of new homes, dramatically reduces soil infiltration and impedes the growth of plants. Compacted soil frequently results in poorly established lawns, which increases the potential for runoff and may drive some new homeowners

to use more lawn fertilizer than homeowners residing in older, more mature developments.

Soil restoration is a technique that can be used to alleviate soil compaction and improve the nutrient retention capacity of soil. The two primary practices associated with soil restoration are tillage and the addition of organic amendments such as compost. The type of tillage that needs to be performed and amount of compost that needs to be added to restore the hydrologic function of soil are dependent on soil type, the depth of soil compaction and the intended stormwater application of area in question. 

If the area will not receive runoff from adjacent impervious areas and compaction is limited to the top few inches of surface it can be alleviated by simply rototilling the soil. A simple rule of thumb when using compost to improve the infiltration properties of soil high in silt and clay is to add compost at a ratio of two parts soil to one part compost. Since most rototillers only mix soil down to depth of six

inches, this means a general purpose lawn area having compacted soil should be amended with about two inches compost prior to turf establishment. 

When compaction extends to the subsoil a multi-shank ripper is used in combination with rototilling to loosen soil and incorporate compost. The ripper breaks up the subsoil or pan layer residing below the operational depth of the rototiller while the rototiller incorporates the compost into the topsoil. A third implement such as a deep angled subsoiler is sometimes used after ripping to break up the top

soil and upper portion of the subsoil without inverting the two.

Use of a multi-shank ripper and subsoiler are rare in residential lots because of the limited maneuverability of the large tractors that are needed to draw these implements through the soil and the presence of buried utility lines on the lot. Smaller more maneuverable tractors can be used to pull single shank rippers through areas of the landscape where the need for restoration of hydraulic function of soil is high. Lawn areas that serve as a filter strip and rooftop disconnection paths are two examples of such areas.

When high volume additions of compost are made to alleviate soil compaction the amount of nutrients added to soil can be substantial. For example, incorporating two inches of a widely available municipal compost created from yard trimmings will add about 60 pounds of nitrogen (N) and 15 pounds of fertilizer grade phosphorus (P) per 1000 ft2 of treated area. The addition of this amount of N and P will reduce or eliminate the need for lawn fertilizer for several years but has raised concerns about the loss of these two nutrients in stormwater runoff.

Studies that have utilized relatively small field plots have reported that the reduction in runoff resulting from the addition of high volume amounts of compost is large enough to result

in reduced N and P losses from lawns when compared to lawns established in a non-composted amended soil. With impervious surfaces often contributing flow to lawn areas, the dynamics of runoff

from residential lots can be very different small research plots. With this in mind we conducted a project within a new residential development in Clarksville, MD, to compare N and P runoff losses from lots amended with a high volume compost prior to turfgrass establishment with lots that did not receive this treatment. The project was funded by the National Fish and Wildlife Foundation.

The Preserve at Clarksville is a near symmetric development consisting of an east and west side where runoff from the backyards on each side of the development is directed to a swale located just beyond the back property line of each lot. The swale behind the lots on the east side of the development has a configuration of drains that allowed us to isolate and collect runoff from two adjacent lots on this side of the development. The new homeowners on this side of the development

permitted us to amend the top 5.5 inches soil in their backyards with 1.9 inches compost after which the yards were seeded with a tall fescue/microclover seed mixture. Microclover is a small leaf clover

that adds N to the soil and was included in the seed mixture to reduce the long term fertilizer needs of the lawn. The two homeowners agreed not to fertilize or apply herbicides to their lawns for the duration of the project.

The swale on the west side of the development received runoff from seven lots. Six of the lots had previously established lawns on them at the beginning of project. A house was built on the seventh lot during the project with the lawn on this lot being established about a year after monitoring of runoff within the development began. We had no input on how homeowners maintained their lawns on this side of development, but did send them a survey at the end of each year of study asking if and when they fertilized their lawns. Three to four homeowners completed the survey each year with two indicating the lawn was fertilized at least twice each year.

Technical difficulties encountered in the first year of study resulted in little useable N and P data being collected during this time. In the latter half of the monitoring period there was no difference in area adjusted N and P load losses from two sides of the development, although there was a consistent trend of higher P load losses being observed from the compost and microclover treated side of the

development. The opposite trend existed in the N data with lower area adjusted N load losses being seen from the compost and microclover treated side of the development for the last six storm events of the project where the concentration of N and P in runoff was measured.

Due to a recent interpretation of the Maryland Lawn Fertilizer Act of 2011 by the Maryland Department of Agriculture, compost is now treated as a fertilizer source. The 2011 law caps the amount of slowly available fertilizer N that can be added on a single date to 2.5 lbs. of N per 1000 ft2. This means that when conventional tillage practices are used to alleviate surface compaction no more than about 1/8 of inch of compost can be incorporated into the soil in areas where lawns are to be established. This is not enough compost to improve infiltration properties of most soils. If ripping or other deep tillage practices are employed to breakup compacted subsoil it is permissible to incorporate high volume amounts of compost into the soil of areas where lawns will be established.

Soil restoration of lawn areas using compost and conventional tillage practices is a recognized stormwater best management practice in the states of Pennsylvania and Virginia with the latter

state providing explicit reductions in the calculation of total volume of runoff from a site with its use. Thus, there is a potential economic incentive for builders in Virginia to use this practice when it provides a lower cost alternative to reducing stormwater runoff than other approved practices that can used to accomplish this goal.

In contrast, the recent interpretation of the Maryland Lawn Fertilizer Use Act will effectively preempt the practice of rototilling soil to depth of four to six inches and amending it with compost to improve infiltration properties of lawn areas in Maryland. This includes lawn areas that serve as disconnection paths unless deep tillage practices are used to incorporate the compost. Other low nutrient containing organic matter materials could be used in place of compost, however, materials like sphagnum peat moss are difficult to work with and may actually increase the need for fertilizer when incorporated into the soil.

The slow release N properties of yard trimmings compost that was utilized in this project produced a lawn with excellent color and density. Lawns possessing high shoot densities are not only attractive but also reduce runoff. With restrictions on the use of compost now in place in Maryland, landscape contractors will now need to go deep with compost incorporation in order to continuing using it as soil restoration material in lawns areas.

Virginia’s Master Gardeners are Making a Difference In Water Quality One Yard at a Time

By Mike Goatley, Professor and Extension Turfgrass Specialist, Virginia Tech

Virginia is fortunate to have several very active Master Gardener Volunteer chapters across its major metropolitan areas.  The state has 62 MG units scattered across the Commonwealth comprised of over 5500 MGVs that made approximately ½ a million contacts in 2014.   These volunteers are organized and led by Virginia Cooperative Extension agents at the county and city levels and they receive extensive training in all areas of horticulture and soil science prior to their ‘graduation’ and designation as a Master Gardener Volunteer through VCE.  Their commitment also includes specified hours of volunteering in civic horticulture.  I have the privilege to provide the turfgrass component of their training for many of the MGV chapters and I consider these volunteers to be my ‘boots on the ground’ to spread the word regarding Best Management Practices in lawn care.

The Chesapeake Bay TMDL program has spurred the interest of many of the MGV chapters to develop committees specifically devoted to urban nutrient management activities.  These MGVs work with homeowners one-on-one, measuring their property, taking soil samples, and then meeting with the homeowner and discussing soil test results and a fertilization program that will result in a healthy lawn that protects the environment, not harms it.  Within the past year all of the urban nutrient management programs were merged under a statewide umbrella program called “Healthy Virginia Lawns”, an effort that will allow for better reporting and documentation of the impact that the Master Gardener Volunteers are making in improving water quality.

There is great interest in the use of microclover as a component of lawns in Virginia.  Research updates from Virginia, Maryland, and Pennsylvania were shared in MGV training programs I conducted for 10 MGV chapters and approximately 400 volunteers across the most populated counties in northern Virginia, Richmond, and Tidewater.  The constant question was ‘Where do I get microclover?”.  There still are some issues in exactly where microclover will thrive in Virginia because the Virginia Tech research at two comparatively warm locations in the state (Amherst and Virginia Beach) provided very mixed results in microclover persistence.  It appears that microclover persistence is going to be a challenge in our warmest regions.  However, microclover has performed very well either as a monoculture or in a mixture with tall fescue in Blacksburg at the Virginia Tech Turfgrass Research Center.  It is anticipated that microclover will thrive in the cooler areas of Virginia, particularly the highly populated northern Virginia locations that are much closer to the University of Maryland research site than the warmer research locations where the work was conducted by Virginia Tech. The excitement of the Master Gardener Volunteers regarding the use of microclover in lawns is because they see the inclusion of this nitrogen-fixing plant material in lawns as a direct complement to their efforts in urban nutrient management programs.

Efforts to incorporate compost into Virginia lawn management programs have been a priority of the Virginia Master Gardener Volunteer programs for the past 10 years.  The demonstrated success in the use of compost as either a pre-plant incorporated soil amendment to urban soils or as a topdressing addition in ¼ inch increments 1-2x per year has been extensively promoted through educational programming and other extension outreach efforts by both myself and our Compost and Biosolids Specialist, Dr. Greg Evanylo. The compost component of this research trial continues to affirm the value of compost as a soil amendment that improves both the physical and chemical properties of the soil and enhances a more sustainable turfgrass management system that requires fewer water and chemical inputs.

In summary, Virginia’s Master Gardener Volunteers are anxious to implement the research findings of the joint Maryland, Virginia, and Pennsylvania research. They believe these findings will continue and enhance their efforts in making a difference in the Chesapeake Bay “one yard at a time”.

Compost Incorporation and Microclover Overseeding in 'Yukon' Bermudagrass

Installation and maintenance of turfgrass requires a number of inputs, including fertilizer application. With the increased concern over nutrients moving into the Chesapeake Bay, especially nitrogen and phosphorus, there is interest in ways to reduce fertilizer inputs. Through a grant funded by the National Fish and Wildlife Foundation’s Chesapeake Bay Stewardship Fund, we are cooperating on a project with the University of Maryland and Penn State in a research project to do just that.

Our research

The overall objectives of the project are to evaluate and promote the adoption of compost incorporation prior to turfgrass establishment as a best management practice, to evaluate the incorporation of compost after turf establishment and to reduce nitro- gen fertilizer use by incorporating microclover at seeding or after turf establishment. Each trial includes four treatments:

• no compost/ no microclover addition

• compost addition without microclover

• microclover seeding without compost

• addition of compost and microclover

A perennial clover that closely resembles white clover, microclover fixes nitrogen, so it may be an alternative to application of nitrogen fertilizers. Within each of the treatments, half of the plot received no additional fertilizer, while the other half received 1 lb. of nitrogen per 1,000 ft2 yearly. Microclover has smaller leaves and flowers than white clover, and thus it may blend better into turfgrass stands (Photo 1).

At Virginia Tech, we evaluated compost addition and microclover seeding in ‘Yukon’ bermudagrass, while the other cooperators evaluated these treatments in tall fescue. Incorporating compost and microclover with bermudagrass seeding should improve the quality, color, quality and greenup of the bermudagrass. Com- post incorporation should improve water infiltration rates.

We established two trials at the research station in 2012, one evaluating the four treatments at seeding time of bermudagrass and the other evaluating compost addition and microclover seeding in established bermudagrass. For all plots, we have been evaluating turf cover, color and quality, as well as water infiltration.

Trial 1

This trial evaluated the aesthetic appeal of a bermudagrass plus micro- clover lawn, with compost incorporation by tilling, with and without N.

Procedures

Plots receiving compost received 2" of the material, spread evenly over the surface and then tilled in with the native soil on June 29, 2012. Plots were seeded on July 2, 2012, with either 2 lbs. ‘Yukon’ bermudagrass seed per 1,000 ft2 or 1.9 lbs. per 1,000 ft2 ‘Yukon’ bermudagrass seed plus 0.1 lb. microclover seed per 1,000 ft2.

No preemergence herbicides were applied in 2012. A March 2013 pre- emergence application of Pendulum 2G (1.5 lbs. pendimethalin per acre) and a late April application of Dimension 2EW (0.25 lbs. dithiopyr per acre) was made for crabgrass control. The preemergence crabgrass treatments were also applied in 2014.

Compost was reapplied in spring of 2014 as a 1/4" topdressing.

Results

Little to no microclover was noticed in any of the plots in 2012. Bermuda- grass establishment was greatly improved with the addition of com- post (Table 1), probably due both to the nutrients released from the compost and to a dilution of the weed seed present in the soil from the volume of compost incorporated. Without the compost, very little bermudagrass was able to establish, due to a dense stand of crabgrass and other weed species. With compost addition, fewer weeds were present, allowing for better bermudagrass establishment. With the incorporation of microclover, the use of herbicides in a bermudagrass lawn becomes very limited, and establishment can be hindered by the onset of summer annuals.

The preemergence herbicides applied in 2013 controlled crabgrass, which had hindered the 2012 grow-in of ‘Yukon’ bermudagrass. Bermuda- grass cover therefore increased from April 2013 to October 2013 in all four treatments, with the highest cover in the compost plots (Table 2). However, the reduction in summer annual weeds also allowed an increase in the natural population of white clover to increase and become more prevalent (Table 3).

As hypothesized in the research goals and objectives, incorporating compost prior to seeding increased turfgrass quality and color (Tables 4 and 5). Infiltration results also showed the benefits of incorporating compost prior to establishment (Table 6). Similar benefits of compost addition on bermudagrass color and quality were seen in 2014 (data not shown).

Trial 2

This trial evaluated methods to intro- duce microclover into existing bermudagrass turf, with compost incorporation by aeration and slicing, with and without N.

Procedures

Plots measuring 15' by 15' were arranged an eight-year-old stand of ‘Yukon’ bermudagrass. Verticutting of the plots occurred on September 5, 2012. Compost was added to plots and raked in on September 7, 2012. The plots were aerated that same afternoon. Plots receiving micro- clover were seeded on September 10, 2012. Plot maintenance in 2013 and 2014 was the same as for the previous trial.

A March 2013 preemergence application of Pendulum 2G (1.5 lbs. pendimethalin per acre) and a late April application of Dimension 2EW (0.25 lbs. dithiopyr per acre) was made for crabgrass control. Plots were mowed twice per week at 2". Half of each plot received 0.5 lb. N per 1,000 ft2 on June 13, 2013, using a 30-0-10 fertilizer containing 30% sulfur-coated urea. Plots were evaluated visually in April, May and June. Initial infiltration data were collected in July.

Results

In trial 2, we were able to establish a stand of microclover (Table 7). Since this was in an existing stand of bermudagrass, we did not have the competition from summer annual weeds that was seen in the newly seeded bermudagrass trial. Compost addition increased the amount of micro- clover compared to no compost. The percent cover of microclover did not change when evaluated in the fall of 2013 and the spring of 2014 (data not shown). Microclover increased green color compared to no microclover for most of 2013 (Table 8), but no improvement in turf color was seen in November of 2013 or April of 2014 from microclover (data not shown). Since bermudagrass goes dormant during the winter, the microclover was very evident and could be considered a weed problem, especially due to the non-uniform distribution of the microclover plants.

Compost addition increased the color ratings of the turfgrass in June 2013 (Table 9, page 28), but the effect wore off, since no benefit to turf color was seen in November of that year. When we reapplied compost later in the spring, turf color was improved (data not shown).

Conclusions

Adding compost at the time of bermudagrass seeding improved establishment. Compost addition to both newly seeded and established bermudagrass improved water infiltration rates and turf color.

Microclover, however, does not appear promising for use in bermudagrass for two reasons. Since selective herbicides are not avail- able for use in newly seeded micro- clover/newly seeded bermudagrass, weed competition will limit the stand establishment for both species. Micro- clover can be established in existing stands of bermudagrass, but a non- uniform appearance of the turf, especially when bermudagrass is dormant but microclover is still growing, may not be acceptable to turf managers or homeowners.

 

New Year Starts off with Microclover Symposium, More to Come

 
The Maryland Turfgrass Council started off the New Year by hosting a microclover symposium as part of its annual Turfgrass Conference. The two day Conference, which brings together turfgrass professionals from throughout the mid-Atlantic serves as the primary turfgrass education event held in state of Maryland each year.  The microclover symposium, which was held on January 5, brought together five university professors who have either been working on integrating microclover into cool and warm season lawn grasses or have extensive experience in the growth and management of clover in pasture systems.

Associate Professor Emeritus and former University of Maryland Forage Extension specialists Dr.  Lester Vough launched the symposium by providing an overview of the difference types of clover and how each has traditionally been utilized in pasture systems.  Dr. David Gardner from the Ohio State University followed with a talk on the potential role of microclover in promoting sustainable turfgrass ecosystems.

Dr. Jeffery Derr from Virginia Tech University, presented results from a multi-year project conducted in Virginia Beach that examined the establishment of bermudagras + microclover lawns from seed and the incorporation of microclover into an existing stands of bermudagrass.   Dr. Peter Landschoot from the Pennsylvania State University followed with similar presentation on the introduction into microclover into existing tall fescue turf and the establishment and growth of a minimally fertilized tall fescue + microclover lawn. As part of his presentation Dr. Landschoot also reviewed the potential for using herbicides to control weeds in tall fescue + microclover lawns. Dr. Mark Carroll from the University of Maryland wrapped up the symposium by presenting the results a survey aimed at determining the aesthetic appeal of microclover based lawns.

The symposium was popular among conference attendees with over 125 individuals attending the afternoon session. Follow up events aimed at providing additional opportunities to see and learn about inclusion of microclover in lawns are planned for this spring in State College Pennsylvania and at U.S. National Arboretum in Washington DC.

 Speakers at the microclover symposium included (from left to write) Doctors Peter Landschoot. Lester Vough, David Gardner, Jeffery Derr and Mark Carroll

2014 BMP UMD Field Workshop Booklet

Reducing Lawn Fertilizer Use and Stormwater Runoff

Comments on a Recent Visit to the Virginia Beach Microclover Demonstration Trials

Last week I had the opportunity to participate in the Virginia Tech Turfgass Field Day at the Hampton Roads Agricultural Research and Extension Center in Virginia Beach. Over the last two years project members Dr. Jeffery Derr, Dr. Mike Goatley and Turfgrass specialist Adam Nichols have been examining the establishment of a microclover bermudagrass lawn from seed, and the practice of overseeding microclover into an existing stand of bermudagrass.  In both trials they are also looking at the effect of compost addition on the presence of microclover in bermudagrass.

In the case of the establishment trial, the soil was either amended with two inches of yard waste compost or was left un-amended  prior to seeding with 2 pounds per thousand square  feet of Yukon bermudagrass, or alternatively, the same bermudagrass variety containing 5% by weight microclover . In the case of microclover overseeding trial, one-quarter inch of compost was applied as a topdressing immediately after seeding and once a year thereafter. Plots not receiving compost topdressing treatment have received urea at yearly rate of one pound of nitrogen per thousand square feet. The establishment trial was initiated in July 2012 and the microclover overseeding trial in September of 2012. The microclover seeding rate in the overseeding study was two pounds of microclover seed per thousand square feet.

Jeff has been sending me regular updates on color, quality and amount of clover present in each of the plots, however I did not grasp how stark the difference in treatments have been until seeing the two trials this past week. In brief, amending the soil with 2 inches of compost dramatically suppressed the presence of clover in the bermudagrass at this site. As can be seen in the first picture below  there is very little clover in a compost amendment plot that was seeded with the 95% bermudagrass, 5% microclover seed mixture. The amount of clover present in this plot is indistinguishable from that of a nearby compost amended plot seeded with 100% bermudagrass at the same time (lower picture).

Compost amended plot seeded with 95% bermudagrass, 5% microclover seed mixture two years ago.

Compost amended plot seeded with 100% bermudagrass two years ago.

It is likely that the enhanced availability of nutrients associated with the incorporation of compost (i.e., mostly nitrogen) favors bermudagrass growth and establishment over that of microclover.  Dr. Derr also noticed that there was much less weed competition within the compost amended plots compared to the non-amended plots during establishment. The reduced level of weed competition in these plots may have also favored bermudagrass establishment over microclover establishment. Microclover and regular old white clover are present throughout the plots that were not amended with compost. This reinforces my belief that the lack of clover cover seen in the compost amended plots is primary due to the enhanced availability of nitrogen in these plots.

What stood out to me when viewing the overseeding trail was that in plots overseeded with microclover but not topdressed with compost, the presence of the microclover resulted in a darker colored turf than in plots that were devoid of microclover. At this field station stop however Adam Nichols was quick to point out that the primary difficulty with overseeding microclover into bermudagrass is the inability in obtaining a homogenous mixture of the two species. The appearance of the plots overseeded with microclover (with or without the compost topdressing treatment) could best be described as “a patchy mosaic” of microclover within the plot. If the approach of using microclover to reduce lawn fertilizer use in bermudagrass is ever to gain favor, it appears that obtaining something close to an homogenous stand of the two species will require more than a onetime overseeding of microclover into bermudagrass.

Labeled plot in foreground was overseeded with microclover 21 months earlier while labeled plot in background was not. The annual amount of fertilizer applied to both plots is one pound of urea nitrogen per thousand square feet.

Your Microclover Questions Answered (Part 1)

I recently received an email from a user of microclover in Spokane, Washington.  He asked several good questions about microclover in his lawn, and I will try to address these one-by-one in the next three or four blog posts.

Last year, I was looking for a low maintenance lawn alternative and seeded microclover directly into a neglected lawn (mostly weeds) this past spring.  The clover has grown in quite nicely, and although other weeds still are prevalent, I have been mostly pleased with these rich green, no-watering, shade tolerant, nitrogen-fixing plants. I have a few follow-up questions I thought you may be qualified to answer, given your research into this new variety of clover.

Question 1. Since microclover does not flower, I am concerned about it maintaining a long-term presence in my lawn. Will the current plants die after a couple years, or once established, will it remain perpetually, all other things constant? If the former, do you have any ideas for how to maintain a long-term clover presence?

The first thing I should mention is microclover DOES produce flowers.  You may not have seen them yet because of where you are located, the time of year, weather conditions, or perhaps the fertility level of your soil. However, I have observed flowering in my plots in Pennsylvania beginning in late May and lasting through June and into July.  The attached photo shows fewer flowers in plots amended with compost than in non-amended plots.  This is likely due to more soil nitrogen in the compost plots (microclover appears to produce fewer flowers when an abundance of nitrogen is present). One other interesting observation: I saw much more flowering last year compared to the year.  I’m not sure why, but it could be due to differing weather conditions between 2013 and 2014, or the age of the stand.

If your microclover is not producing flowers, don’t be concerned about persistence.  Microclover lives year to year as a perennial, and can spread around your lawn via above-ground runners (stolons).  It survives heat and drought, as well as tough winters.  I was concerned this spring when I saw some dead patches of microclover in my plots (killed by the extremely cold and icy conditions during the winter of 2014).  However, most of the clover survived and gradually filled in the dead patches. Of course nothing lives forever, and it’s possible the clover will eventually fade from your lawn. Extreme drought, excessive traffic, too much nitrogen, and broadleaf herbicide applications are factors that can negatively influence persistence of your microclover.  The longevity of microclover in lawns is something I hope to examine over the next several years. 

The Application of a Mathematical Model to Extrapolate Study Results to Other Locations

Environmental models are used to simulate or reproduce real world conditions and how those conditions change due to varying input. Modeling enhances our ability to extrapolate results from intensively-studied test sites to other potential use sites. These models are used by industry and governmental organizations alike to support scientific analyses.

Input will vary based on the model being used and conditions the modeler would like to simulate, but it can include changes in land use, land management techniques, weather data, etc. The model ArcSWAT 2009 is being used to simulate conditions at the Maryland sites and to show how the incorporation of BMPs (i.e., adding compost to the soil and using a lawn seed mixture containing microclover) affects runoff.

Specifically, ArcSWAT is currently being used to model runoff characteristics from the Clarksville, Maryland test and control sites. ArcSWAT is an interface between Esri’s ArcGIS Geographic Information System and the SWAT model (Soil and Water Assessment Tool) developed by Dr. Jeff Arnold of the USDA Agricultural Research Service. SWAT is a physically-based model, which means it relies on soil, elevation, land use, and weather data to simulate water and sediment movement as well as nutrient cycling within a watershed. Therefore, it allows one to examine how various management methods affect runoff. Subbasins of the watershed are divided into hydrologic response units (HRUs), which are areas of similar elevation, land use, and soil data. Ultimately, the model simulates loadings from each HRU to the stream on a daily, monthly, or annual time step.

The Clarksville test and control sites’ watersheds have been delineated using ArcSWAT. We are currently working on refining input variables in order to accurately simulate water, sediment, and nutrient movement at each site. Once the input is complete we will be able to run the model and compare the modeled results with the results of the on-going monitoring. Ultimately, when the model is appropriately calibrated, the results will be extrapolated to other sites throughout the Chesapeake Bay watershed.