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Landfill diversion of organic wastes through composting is making compost products available for agricultural and horticultural crops. On certified organic farms, nonsludge green waste and manure composts are widely used because the use of these products removes harvest date restrictions imposed by the U.S. Department of Agriculture when raw manure is applied. We quantified several pathogens in point-of-sale composts from 94 nonsludge facilities processing 2.2 million m3 year(-1) of recycled green waste. Only one compost contained Salmonella (1.8 most probable number [MPN]/4 g), 28% had fecal coliforms exceeding the Environmental Protection Agency 503 sludge hygiene limits (1000 MPN g(-1)), and 6% had detectable Escherichia coli O157:H7. In 22 of 47 samples, very low levels of Listeria spp. were found. However, in one sample the Listeria level was very high, coinciding with the highest overall level of all pathogen indicators. Seventy percent of the compost samples were positive for Clostridium perfringens, but only 20% of the samples had levels >1000 CFU/g. All samples were positive for fecal streptococci, and 47% had >1000 MPN g(-1). Statistical analyses conducted using documented site characteristics revealed that factors contributing to elevated pathogen levels were large facility size, large pile size, and immaturity of compost. Application of the California Compost Maturity Index distinguished compost products that had very low levels of E. coli from those with high levels. Products produced with windrow methods were of higher microbiological quality than were those produced with static pile methods, and point-of-sale bagged composts scored very high. These data indicate that compost that is hygienic by common standards can be produced, but more effort is required to improve hygiene consistency in relation to management practices.

DAS-40278-9 maize, which is developed by Dow AgroSciences, has been genetically modified to express the aryloxyalkanoate dioxygenase-1 (AAD-1) protein and is tolerant to phenoxy auxin herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D). To understand the metabolic route and residue distribution of 2,4-D in DAS-40278-9 maize, a metabolism study was conducted with C-radiolabeled 2,4-D applied at the maximum seasonal rate. Plants were grown in boxes outdoors. Forage and mature grain, cobs, and stover were collected for analysis. The metabolism study showed that 2,4-D was metabolized to 2,4-dichlorophenol (2,4-DCP), which was then rapidly conjugated with glucose. Field-scale residue studies with 2,4-D applied at the maximum seasonal rate were conducted at 25 sites in the U.S. and Canada to measure the residues of 2,4-D and free and conjugated 2,4-DCP in mature forage, grain, and stover. Residues of 2,4-D were not detectable in the majority of the grain samples and averaged<1.0 and <1.5 μg/g in forage and stover, respectively. Free plus conjugated 2,4-DCP was not observed in grain and averaged <1.0 μg/g in forage and stover.

The practice of composting mixed green wastes from community collection programs has been on the increase as a means to reduce organic debris to landfills. Recent reports of plant injury have appeared and were attributed to residues of the herbicide clopyralid in compost. Phytotoxicity issues with compost have been reported previously to result from other factors, including heavy metal content, soluble salts, organic acids and oxygen deprivation related to incomplete decomposition. The recent reports of plant injury due to clopyralid-contaminated compost were also associated with very heavy applications of compost, yet few of these reports included observations of herbicide symptomology. Since immature compost may contain sufficient degradation intermediates, soluble salts and other contaminants to cause phytotoxicity, particularly when applied at heavy rates, an effort must be made to distinguish confounding factors. Complete composting normally allows for the degradation of phytotoxic intermediates and synthetic compounds, such as herbicides, as well as allowing for leaching of salts. Absence of compost completeness standards within the compost industry leaves such factors to the guesswork of the end-user. Recommended compost use rates have established a relationship between compost maturity, application rate and use pattern, based on compost quality metrics. Greater attention to the use of high-quality compost, properly designated as to completeness of composting and applied at appropriate use rates, would minimize the potential for phytotoxic effects, irrespective of the contributing source.

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