Organic fertilizers are good, but there’s always the possibility that too much of a good thing is not so good. A recent study conducted by a team of researchers from the Autonomous University of Barcelona (UAB) Centre for Ecological Research and Forestry Applications (CREAF) concludes that organic fertilizers like composted sewage sludge and animal waste might be toxic to soil organisms when applied in excess.
Not only might excessive amounts of these fertilizers be detrimental to invertebrates and soils microorganisms such as earthworms, annelids, they could also be dangerous for the plants themselves and should be monitored so they can be used at appropriate levels for common crops such as red clover, field mustard, and perennial ryegrass, the three that were studied by the researchers. The research group was able to determine the “safe dose” of applied organic fertilizers such as dehydrated sewage sludge, two kinds of composted mud, two kinds of heat-dried mud, and one sample of heat-dried pig waste.
The researchers found that the main source of toxicity was instability of organic fertilizers, which, as they rapidly decompose generate ammonia as a byproduct and th main source of the toxic effects observed in the soil organisms. The main takeaway according to the researchers is that “eco-toxicological criteria should also be included in legislation in order to prevent the environmental impact caused by the use of organic residues”.