Microclover - Tall Fescue Lawns in the Mid-Atlantic Region

Amending Soil with Compost to Reduce Stormwater 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.

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. 

Lawn Establishment: A Reality Check from the Showcase Site

In my introductory turfgrass management course I always stress the importance of establishing cool season turfgrasses in the fall of the year. Seeding turfgrasses, such as tall fescue, in September or early October offers the advantages of near optimal soil temperature for seed germination, less weed and disease problems and greater retention of soil moisture during early seeding growth due to declining temperatures and day length. Implicit in my discussion of this topic is that one has a choice of when they will establish their lawn. Nothing could be further than the  truth for a Home Builder. Lawn establishment in new residential developments usually occurs in a relatively narrow window between the time the finished grade is created on a lot and the sale of the home. Lawn establishment has to occur during this window because sediment and erosion control plans almost always stipulate that soil stabilization on the lot needs to occur before transfer of the property to the new owner can take place.

In northern climates it is usually permissible to stabilize the soil for late fall to early spring property closings by placing straw or another type of erosion control material over the seed. For the remainder of the year though vegetative stabilization of the soil needs to occur in advance of transfer of the property. This means that cool season turfgrasses are sometimes seeded at the worst possible times of the year. This was clearly the case for the two residential lots that were seeded at the project showcase site. One lot was seeded on May 29, 2012 and the other on July 3   2012. Since neither lot possessed in ground irrigation, lawn establishment was completely dependent on natural rainfall. Rainfall during this time of year typically comes in form of thunderstorms and the summer of 2012 was no exception to this type of precipitation pattern. 

 The contractor placed down what I thought was an unusually thick layer of straw ( 3 inches uncompressed)  over the 95% tall fescue 5% microclover seed mixture that was broadcast in May . I was concerned that this much straw would inhibit the growth of microclover seedlings so I had the contractor cut the amount of straw  blown over the seedbed by about a third in the July seeded lot. After a couple of severe thunderstorms had passed through the area it became apparent why the contractor had placed so much straw down in May. Three inches uncompressed straw did a good job minimizing erosive losses and seed washout. Putting down two inches of straw was much less effective at minimizing washout, especially in areas where runoff tended to be limited to sheet flow only. Neither of two depths of straw was effective stopping erosive losses in areas of two yards where flow became channelized.  

                By October, the lawn seeded in May looked great. The July seeded lawn was still struggling to achieve full soil surface coverage due to the seed wash out that occurred over the summer.  Did straw thickness affect the establishment of the microclover? There was a fair amount of microclover present in the May seeded lawn by the end of summer. However, because of the seed washout that occurred in the July seeded lot, it was difficult to determine if microclover establishment was influenced by amount of straw placed in the seedbed. To get a better handled on the effect of straw cover on microclover establishment we will be conducting a study at the University of Maryland Paint Branch Turfgrass Research Facility this fall to see how the amount of straw cover affects the establishment of a tall fescue+ microclover lawn seed mixture. This study is one of the several microclover management studies that will be discussed at the 2013 University of Maryland Landscape Contractor Field Day. For those interesting in attending this field day, it will take place on Wednesday October 23, at the University of Maryland Paint Branch Turfgrass Research Facility, in College Park, Maryland.

Lawn  composition ten weeks after a 29 May seeding of a 95% tall fescue, 5% microclover lawn seed mixture.