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different sites. The highest concentrations ++ere found in
<br />Composts produced at sites in the most urban areas. Gener-
<br />• ~ ally it has been considered safe to use garden produce grown
<br />in soils with total least levc•Ic less than it-tt nrt; Lt; (parts per
<br />millionl. The lead levels in the yard ++•acte conrpostc are con-
<br />sidcrahly less than this wggested limit. (rther trae e nu•tals
<br />such as cadmium, nickel, copper, chmmiunr, and zinc arr
<br />also present in compost in small duantitie~. Ibe h1inneu,ta
<br />Pollution Control Agency has estahlishc•d ma~cimum c on-
<br />centrations ofthese elements for compacts that arc• applied to
<br />soil. The allowable levels in milligrams per kilnt;ram on a dry
<br />weight basis are:
<br />Cadmium 10
<br />Nicke! 100
<br />Copper 500
<br />Chromium 1000
<br />Zinc 1000
<br />Typical concentrations of these elements found in municipal
<br />yard waste composts are many times less than the allo++•able
<br />levels.
<br />Use of Compost as a Soil Amendment ,~~'~~
<br />Compost is used as an organic amendment to improve physi-
<br />cal, chemical, and biological properties of soils. Adding
<br />compact will increase the moistum hr,ldinc capacity of
<br />sandy soils, thereby rcclucing druut;ht rl,rnr,rt!r• to t,lant>.
<br />When added to heavy clay soils, compost will improve
<br />drainage and aeration, thereby reducing ~+atr•rlogging dam-
<br />age to plants. Compost will increase the ability crf the sail to
<br />hold and release essential nutrients. The actin ity of earth-
<br />worms and soil microorganisms beneficial to plant gro+vth
<br />will be promoted with compose additions. Other benefits of
<br />adding compost include improved seed emergence and wa-
<br />terinfiltration due to a reduction in soil eructing.
<br />Over time, yearly additions of compact +vill curate desirable
<br />soil structure, making the soil much easier to ~+ork. For im-
<br />proving soil physical properties, add ant in r,rl,or~te 1 - 2
<br />inches of well decomposed compost in the tot, f, - 8 inches of
<br />soil. Use the lower rate for sandy soils and the higher rate for
<br />clay soils.
<br />To a limited extent, compost is a source of nutrients. How-
<br />ever, nutrient release from compost is slow and the nutrient
<br />content is often too low to supply all the nutrients necessary
<br />for plant growth. As noted in Table 3, there is a ~+ ide variation
<br />in nutrient content of municipal leaf compost. Differences
<br />are probably due to several factors including ace of the com-
<br />post, amount of water added, plant species, and the amount
<br />of soil that becomes mixed into the pile during turning.
<br />h is usually necessary to supplement compact +•. ith some fer-
<br />tilizer,particularly nitrogen. If the Uh ratio of the• compost is
<br />less than 20 to 1, nitrogen will tend to tie released rather than
<br />tied up f5). For the majority of municipal +ard wade com-
<br />posts,the C/N ratio is less than 20 to t cTahlc• 3 ~. Thus, ++hile
<br />compacts may not supply significant amount. of nitrogen,
<br />especially in the short run, nitrogen -ie-ut~ -!~~ Auld not be a
<br />major concern with most yard ++actc• c on,{~~~~tc.:'iptrrrrxi-
<br />mately t cup of ammonium nitrate tt) t ~ Ib ac foal nits r};ent
<br />per 3 bushels f 1 OU Ihs c c>mpoct) is rcvturrrrl r, ~ t~•o~ ide the ad-
<br />ditional nitrogen nrc•dcd by most garclc•n t~l,tn~~.
<br />Have your soil ttlstr•d every fe++ years 1.. dc•h•ntrine +ylu•tlter
<br />supplemental l~ltosphorus and potassium are required. The
<br />pH of most yard waste composts is usually between 7.0 and
<br />B.O.This slightly alkaline pH of compost should not pose any
<br />prohlents when dilutrd by mixing into the soil and in fact is
<br />bene(ic ial to plants gro+rinf; on acid soils. Because of the al-
<br />kaline pH,yard wash comps nts do not appear wet! soiled for
<br />uu• on ac id Coring plants c-ich as azaleas and blueberries.
<br />Use of Com~wst in Putting Soils
<br />Leaf c ontpuct c an be used ac a component of potting mixes.
<br />Generally, no etc rre than one ctuarter to one third by volume
<br />of the potting mix should be compost: over time some of the
<br />compost is likely to decompose and the volume of the pot-
<br />ling soil will Ix• reduced. In aeldition, high levels oicompost
<br />in a mix may cause waterlogging and poor aeration for roots.
<br />Although proper composting destroys most weed seeds and
<br />disease organisms, some may still survive due to incomplete
<br />mixing. To obtain a completely pasteurized leaf compost, it
<br />is necessary to heat the material in an oven unfit the tempera-
<br />ture of the center reaches 160"F and is maintained for 30
<br />minutes.
<br />Use of Cornpvst as a l~lulch
<br />Mulches are used in gardens to suppress weeds, reduce soil
<br />c~re,cinn, mcxli(y the coil teml,erature (cooler in the summer,
<br />+varmer in tlt<• +rintc•r}, and consen•e soil moisture. Yard
<br />waste compost makes an ideal mulch for annual and peren-
<br />nialgardens. All that needs to be done is to apply a 3 - 6 inch
<br />layer of comlxst around the base of the plant. Periodically
<br />throughout the summer, you ntay need to add more compost
<br />over the old layers to maintain the benefits of the mulch.
<br />The soil em~ironment beneath the mulch is favorable for
<br />promoting earth~rorms ~+ hash in turn are valuable for aerat-
<br />ing the soil. Organic matter is gradualh added to the soil as
<br />the mulch decomposes. For annual gardens, the mulch can
<br />be worked into the soil at the end of the season to further im-
<br />prove soil physical prolerties. For perennials, it maybe ben-
<br />eficial to remove the mulch in the spring to allow the soil to
<br />thaw out faster. As discussed above, a well decomposed yard
<br />waste compost will not tie up nitrogen. Therefore, additional
<br />nitrogen beyond that recommended for plant growth is un-
<br />necessary. If uncomposted or partiaHycomposted leaves are
<br />used, one tables{x~on of a (ti{;It nitrogen fertilizer should be
<br />applied to each bushel of mulch.
<br />Alternatives io Compostiti+g Grass Clippings
<br />The question of whether to ss c) ip-
<br />prngs as been around for Ion tiro .However, it is now
<br />agr tat as long as the grass is not excessively long and
<br />clippings do not thickly cover the lawn surface after mowing,
<br />there is normally no need to collect the clippings. Aside from
<br />reducing the work im•olved in lawn maintenance, leaving
<br />the grass clippings benef its the turf by returning nutrients and
<br />organic matter to the soil. If evenly distributed, clippings left
<br />on the la++•n can Ix~ eyui+alent to one fertilizer application
<br />per year.
<br />In order to keep your lawn looking healthy and to control the
<br />amount of c tappings generated, several maintenance prac-
<br />tices should he tollo+red. It is important that mo++•ing height
<br />be prolx~rly adjusted. The height of the cut ++ill depend on
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