Ground soils support vegetation in terrestrial ecosystems and all crops that are the basis of our food. These soils are degraded by erosion, salinization, and loss of organic matter, which occurs due to excessive tillage. It takes between 100 and 400 years for one centimeter of surface area to be formed by weathering processes. Approximately 77.4 percent of the affected national surface is associated with agricultural and livestock activities.

Soil supports vegetation in terrestrial ecosystems, and thus all the crops that are the basis of our food. It is responsible for filtering rainwater and retaining it so that it is available for plants, in addition to retaining the liquid in the space where the roots develop and thus supplying it to plants when it is not raining, explained Christina Siebe Grabach, a researcher at the Institute of Geology (IG) of the UNAM.

If it is healthy, it can infiltrate an important part of the rainwater and prevent it from draining over the surface, which could cause erosion, which is one of the main problems of deterioration, whether by water or wind, as well as salinization, which occurs when irrigating with poor quality liquid and has many soluble salts and the loss of organic matter, which happens when there is excessive tillage.

Some figures

In Mexico, urban areas and human settlements occupy an area of approximately 1.85 million hectares, according to INEGI data. According to figures from the Ministry of Environment and Natural Resources (SEMARNAT), in 2002 about 77.4 percent of the degraded national surface was associated with agricultural and livestock activities (38.7 percent each) and 16.4 percent with deforestation and vegetation removal. The rest of the country's degraded area (around 5.3 million hectares, 6.1 percent of the total affected area) is due to urbanization, overexploitation of vegetation, and industrial activities.

At the state level, these activities have a different impact. Agricultural activities contribute most to degradation in Aguascalientes (85.4 percent of its degraded area is due to this cause), Hidalgo (83.4) and Tlaxcala; overgrazing in Chihuahua (71.2 percent), Sonora (55.5), and Durango (52.5). 5) and Durango (52.2); deforestation in Nayarit (42.8 percent), Campeche (38.6) and Chiapas (35.6), and urbanization in Mexico City (65.6 percent), Baja California Sur (29.8) and Baja California (26.2).

It is better to prevent it because it takes a long time to rehabilitate them. One centimeter of soil to be formed by weathering processes requires between 100 and 400 years depending on conditions. Many processes lead to the loss of several centimeters in a single growing season. When there are bad management practices, up to 5, 10, or more centimeters can be eroded, and this cannot be recovered in a short time; it would be necessary to wait hundreds or even thousands of years to have surface formation again.

Efforts at UNAM

In the Soil and Environment working group of the Institute of Geology, Siebe and her colleagues work in the field to carry out various studies of the state of the soil and its effects due to human participation in it. "First we make an evaluation of soil quality, a diagnosis, and then we issue recommendations to improve management practices and adapt them to avoid degradation," she said.

In an observatory in Valle del Mezquital (Hidalgo) they determine how the characteristics change due to irrigation with wastewater. It is an important resource because it provides liquid and nutrients to a semi-arid zone that was previously not very productive. However, the water resource also carries pathogenic organisms that can cause disease, and contains contaminants. Its surfaces have a good capacity to filter and retain them; when overloaded, they allow heavy metals or the spread of antibiotic drugs and resistance genes, an issue of public health relevance, to pass through to crops.

Siebe and her group chose this place for their study because it is an area that receives runoff and wastewater from the metropolitan area of the Valley of Mexico, and worldwide it is the largest and most continuous area where wastewater is applied for irrigation, which makes it a laboratory where the processes can be studied very well, detect which are beneficial and which are risks, determine the carrying capacity of soils and how they can filter both nutrients and pollution. More attention needs to be paid to the soil because in general society has a vague perception of what it means for the life of people, other species, and the planet in general. There is little information about what it means to have good quality soil.

Large-scale impacts

Unfortunately, there is no precise information on the amount of area affected in Mexico. The Ministry of the Environment and Natural Resources (SEMARNAT) published data in 2009 that speak of up to 75 percent of the territory damaged, but the methodology used for these estimates is questionable. Work is currently underway to improve it, said the researcher. Alarming loss data are reported worldwide, so much so that the FAO has launched a very strong initiative (Global Soil Partnership) to warn about extinction and promote conservation programs at all levels.

Climate change exacerbates erosion processes as extreme rainfall events have a higher erosiveness, water scarcity will leave the land without irrigation and thus without cover, which may increase wind and water erosion. The change in the length of the growing season, especially if it is shortened, can also increase vulnerability to erosion. Lack of water in coastal areas can promote overexploitation of aquifers, which in turn promotes saline intrusion, leading to the use of water with higher salt content for agricultural irrigation.