Organic sources of nutrients and human health

Agronomists generally consider integrated plant nutrient management – which entails the complementary use of organic sources of nutrients and manufactured fertilizers – to be optimal, where the possibility exists. The combination of both sources of nutrients makes it possible to achieve the greatest net improvement in the physical, chemical and biological aspects of the soil.

Plants can only absorb inorganic forms of nutrients. This means that any organic forms of nutrients must be converted into inorganic forms before they can be used by plants. Given this fact, it is not surprising that reviews of statistically valid studies on the impacts of different sources of nutrients on the nutritional content of crops indicate little or no difference . Other factors, such as cultivar, location, weather and freshness seem to have much more influence on nutritional content. (Boume and Prescott 2002)

Like any agricultural input, organic sources of nutrients have both advantages and disadvantages. Appropriate management is necessary to manage the associated health risks.

Urban composts and sewage slurries may be contaminated by toxic organic compounds and heavy metals. These sources of nutrients either need to be treated to remove the contaminants or to be used on non-food crops.

Sewage and farmyard manure needs to be properly treated in order to eliminate the possibility of bacterial contamination of food crops or of groundwater.

Indiscriminate use of animal manures and human waste (sewage sludge) can create human health hazards through the accumulation of heavy metals and pathogens in the soil.

Unnecessarily high applications of manure can lead to excessive nitrate (NO₃^-) leaching to groundwater. (Although there is significant debate about whether nitrate in groundwater is, in fact, a health risk.)