Agriculture Reference
In-Depth Information
and others (2004, 2005) concluded that the NOP 120-day minimum for manure appli-
cation to harvest interval cannot guarantee the absence of
E. coli
on vegetables such
as carrots and lettuce grown in Wisconsin. Their results also emphasized that the
fertilization-to-planting interval is a factor affecting produce contamination more
important than the fertilization-to-harvest interval because seedling emergence is more
susceptible to pathogen internalization.
Control of Pathogens in Animal Manure by Composting
Animal manure, if not properly contained or treated, can be a major source of water-
borne and foodborne illnesses. Therefore, the question of how to eliminate the persis-
tence of pathogens in animal manure or manure-amended soil should be a major
concern for animal waste management practices. Animal production establishments
may handle the animal wastes in different ways, depending on the types of manure,
farm facilities, and physical condition of the farm. Treatment of animal wastes gener-
ally falls into three categories: physical, chemical, and biological (CAST 1996; Sobsey
and others 2001). Types of waste treatment facilities include lagoons, composters,
solid separators, settling basins, and vegetative treatment systems (Meyer and others
1997; Berry and others 2007). The following section focuses on the process of com-
posting to inactivate pathogens in animal manure.
Composting
Composting is frequently done to convert agricultural wastes into organic fertilizers,
soil amendments, or growth medium for greenhouse plants (Rynk 1992). Compost
amendments reduce the bulk density of soil, improve soil tilth, facilitate more vigorous
root growth, and suppress plant diseases by directly or indirectly affecting plant
pathogens or host capacity for growth (Boulter and others 2002).
Composting is a managed process in which manure and other organic materials are
digested aerobically and anaerobically by microbial action. The composting process
generally goes through four phases: mesophilic, thermophilic, cool down, and matur-
ing. At each phase, microbial populations vary signifi cantly as affected by changing
environmental conditions. The heat (50 ° to 70 °C) generated in the process can kill
many microorganisms (including human and plant pathogens), weed seeds, and fl y
larvae. Additionally, composting has been explored as a potentially safe process for
preventing horizontal resistant gene transfer by inactivating genetically modifi ed
organisms or degrading antibiotics in animal wastes (Singh and others 2006; Arikan
and others 2007).
According to a US SAC report (1998), there are no national standards for
composting animal manure. USDA prescribes to organic growers that composting
operations maintain a temperature in the range of 55-70°C for a minimum of 3
days for static aerated pile or in-vessel systems and 15 days with 5 turns for
windrow systems, provided the carbon-to-nitrogen ratio (C:N) is in the range of
25 : 1 to 40 : 1 (NOSB 2002). However, there is limited information regarding the fate
of foodborne pathogens during the composting process in compost, or scientifi cally
based data regarding the optimal conditions for composting manure to kill pathogens
on the farm.
