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Table 2. Approximate concentration of nitrogen and carbon to nitrogen (C/N)' ratio of various materials used in municipal and backyard composts (4) Nitrogen C/wt/wttlo Material % dry we'isha Grass clippings 2.15 20 Leaves 0.5.1.0 40-80 Sawdust 0.11 511 Wood (pine) 0.07 723 Fruit wastes 1.52 35 Paper 0.25 170 Table scraps - Is *See text for further explanation. Municipal Composting of Yard Wastes If budding your own compost pile is impractical, there are municipal composting sites available in many counties for disposal of leaves and grass clippings. Depending on the lo. cation, leaves only or leaves and grass clippings may be dropped off at the composting sites. Some city compost pro- grams also have curbside pick-up in the fall. Completed compost is also available free of charge from these sites, and some sites have free delivery of quantities over 10 cubic yards. For information on the nearest composting site, con- tact your local county extension agent. In the past there has been some concern about using munici- pal waste compost because of contamination with lead and other trace metals. Possible modes of yard waste contamina- tion may be due to direct exposure of leaves and grass to au- tomobile exhaust or to inclusion of street sweepings (which might contain ;.igh levels of lead from automobile exhaust) in the compost pile. A study at the University of Minnesota (5), characterized elemental composition of yard waste composts from 11 different sites in the seven -county metropolitan area. The mean and ranges of elemental con- centrations in the compost piles over two years are presented in Table 3. There was a wide range in lead values from the r._ Table 3. Chemical Characteristics of Municipal Yaid Waste Composts: Mean of 17 compost sites over 2 years (5) Concentration (dry weight basis) Mean Range Carbon % 19.3 4.4 - 41.4 Nitrogen % 1.26 0.33- 4.2 Carbon/Nitrogen' 17 It - 25 Phosphorus % 0.19 0.05- 0.5 Potassium % 0.39 0.04- 2.71 Calcium % 3.02 0.70- 8.04 Magnesium % 0.54 0.09. 1.34 Iron % 0.25 0.06- 0.31 Aluminum % 0.27 0.06- 0.31 Manganese mg/kg 420 223 -1261 Sodium mpvkg 154 36 - 921 Zinc mg/kg 88 39 - M5 Copper mg/kg 11 3 - 143 Boron mg/kg 41 7 - 141 Lead mg/kg 49 1 - 330 Cadmium mg/kg 0.4 <0.1 - 1.4 Chromium mg/kg 6.3 1.2 - 52.5 Nickel mg/kg 7.3 1.7 - 33.3 pH 7.6 4.5 - 8.3 'Ratio of carbon to nitrogen (See text for further explanation). <means "less than." '•mg/kg=milligrams per kilogram, which is the same as parts per million