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i <br /> <br />Table 2. Approximate concentration of nitrogen and carbon to nitrog en (C!N)* ratio of various <br />materials used in municipal and backyard composts (4) <br />Nitrogen C/N ratio <br />Material % dry weight wVwt <br />Grass clippings 2.15 20 <br />leaves 0.5 - 1.0 40-80 <br />Sawdust U.1 1 511 <br />Wood (pine) U.U7 723 <br />Fruit wastes 1.52 35 <br />Paper 0.25 170 <br />Table scraps - 15 <br />'See text for further explanation. <br />Municipal Composting of Yard 4Vastcs , <br />If building your own compost pile is impractical, there are <br />municipal composting sites available in many counties for <br />disposal of leaves and grass clippings. Depending on the lo- <br />cation, leaves only or leaves and grass clippings may be <br />dropped off at the composting sites. Same cite compost pro- <br />grams also have curbside pick-up in thc~ fill. Completed <br />compost is also available free of char~e• (r<rnr thc~ce sites, and <br />some sites have free delivery of yuantitic~s over 1U cubic <br />yards. For information on the nearest composting site, con- <br />tact your local county extension agent. <br />C. <br /> <br />In the past there has been some concern about using munici- <br />pal Haste compost because of contamination with lead and <br />other trace metals. Possible modes of yard waste contamina- <br />tion may be due to direct exposure of leaves and grass to au- <br />tomobileexhaust or to inclusion of street sweepings (which <br />might contain high levels of lead from automobile exhaust) <br />in the compost pile. A studv at the University of Minnesota <br />(5), characterised elemental composition of yard waste <br />cvmpo~ts from 1 1 differr~nt cites in the seven-county <br />metropolitan area. The mean and ranges of elements) con- <br />centrations inthe compost piles over hvo years are presented <br />in Table 3. The~rc~ ~~~as a H~idc• range in lead values from the <br />Table 3. Chemical Characteristics of Municipal Yard Waste Composts: <br />Mean of 11 compost sites over 2 years (5) <br /> Concentration (dry weight basis) <br /> A 1c~an Ran ge <br />Carbon °0 19.3 4.4 - 41.4 <br />Nitrogen % 1.26 U.33- 4.2 <br />Carbon/Nitrogen' 17 11 - 25 <br />Phosphorus °l° U.19 ~ 0.05- 0.5 <br />Potassium °~ U.39 U.t~4- 2.71 <br />Calcium % 3.U2 O.-U- 8.04 <br />Magnesium % U.54 (1.11`1- 1.34 <br />Iron °!° 0.25 U.t1b- 0.31 <br />Aluminum % U.2: (1.t-tr- 0.31 <br />Manganese mg/kg 42U 2?3 -1261 <br />Sodium mg,'kg 154 3h - 921 <br />Zinc mg/kg 88 3~1 - 585 <br />Copper mg%kg 1 1 .i - 143 <br />Boron mg%kg 41 - 1-11 <br />lead mKikg 4y 1 - 38U <br />Cadmium mg'k); 0.4 ~ U I - 1.4 <br />Chromium mR'k}; ti.3 1 ' - 52.5 <br />Nickel mg'kK %.3 t .- - 33.3 <br />pH '.t, -1.~ - 8.3 <br />'Ratio of carbon ter nitre~};cn t5~~~ 1t•~t I~~~ turthc~r e~~planativnl. <br /><meanc '•lesc than." <br />"mK'kR=milligrams Ix~r kilot;rinr ~~ hir h is the same as parts per million <br />