Stone-filled landscapes: about soil erosion and places where stones grow

This blog was written by Ángel Héctor Hernández Romero. Facultad de Ingeniería en Sistemas de Producción Agropecuaria, Universidad Veracruzana (Agricultural Production Systems Engineering, University of Veracruz).

Some years ago, while attending a workshop with farmers in a little indigenous village in Los Tuxtlas Natural Reserve with some colleagues and students from the State University of Veracruz (Southern Mexico, at North America), something caught my attention. A farmer pointed out that the stones on his land seemed to be growing. “I prepared my land for the maize season. I applied my liquid (what local farmers call herbicides), I sowed my seeds, I added fertilizers, and some months after, I harvested my corn; I have done this for five years, and the only thing that has grown are the stones. Do you believe me?" he said. We were curious and went to his farm. We immediately noticed that the stones were bigger than they were some years before. What was actually happening was the loss of soil by water erosion (Fig 1).

Figure 1. A stone filled landscape. Ejido Soteapan, southern Mexico.

Soil erosion is one of the most serious problems in the region, with rainfalls of about 2000-4000 mm/year, slopes higher than 20% and clayed soils. The main land uses are coffee and maize croplands and grasslands under conventional management practices that promote soil degradation. Soil losses are measured through direct methods, like erosion pins (Fig 2), and estimated with models such as the Universal Soil Loss Equation. As a result of the conditions described above, an average of 200 tons of soil are lost per hectare and year, and crop productivity is dwindling in a region where people live in remote and marginalized villages.

In this context, as the soil is washed away, year by year, the “growing” stones, roots of some old trees, fences, and some other signs in the landscape emerge from the surface showing the suffered soil erosion; a quantification of the soil lost can be done using the stone height (Fig 3). Furthermore, disappeared wetlands tell us where eroded sediment has been deposited; detached soil reaches the bottom of water bodies, causing siltation of these reservoirs, and finally their disappearing.

Figure 2. A nail or erosion pin used for measuring erosion. Ejido El Tulín, southern Mexico.
Figure 3. A stone that grows about 0.5 inches every year. Ejido El Tulín, southern Mexico.

This is the language we have to translate in order to understand what is happening and what action researchers, students and farmers must take to safeguard our soils. We can protect our soils through better practices such as crop and grazing rotation, agroforestry systems, cover crops, contour lines, terraces and other methods that would give us more efficient and sustainable systems.

The views expressed here belong to the speaker and do not necessarily represent FAO’s views, positions, strategies or opinions.

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