Soil Mapping: Improving Heavy Metal Monitoring

Today's crop, vegetable, and fruit growers face increasingly stringent export requirements.

To guarantee the safety of their consumers, destination countries require detailed information regarding potential contaminants that might be present within agro-exports. For example, they need to clarify whether these foodstuffs exceed the thresholds for toxic heavy metals.

What are heavy metals?

The chemical definition of heavy metals is incredibly broad. However, for the purposes of this article, we can label them as elements that are toxic to living beings. The United States Environmental Protection Agency (EPA) most commonly regulates five main heavy metals: cadmium, mercury, lead, arsenic and chromium.

Unfortunately, heavy metals are present in soils around the world. Heavy metal concentrations occur naturally in soils as constituents of the earth's crust, while heavy metal values can also be influenced by human activities. For example, due to the production of industrial pollutants such as atmospheric contaminants, sewage, mineral fertilizers, pesticides and mining-related pollutants. Heavy metals remain in the soil for incredibly long periods, with a residence time of up to several hundred years.

How can growers identify the presence of heavy metals within their soil? By partnering with crop scientists to conduct rigorous soil mapping.

Soil Mapping Versus Conventional Soil Sampling

Conventional soil sampling uses one or more samples per lot. These are taken at random, following a standard procedure in which several subsamples are drawn around a central point before being homogenized and quartered. Subsequently, a single final sample is obtained.

However, the dynamics of heavy metals in soils can vary significantly, and it is necessary to know their precise distribution throughout the area. This is where soil mapping comes in. Crop scientists must adopt a systematic approach (instead of single composite sampling) to determine the true magnitude of the problem in the field.