Erosion y escurrimiento en parcelas de tepetate t3 en Texcoco, México

The reclamation of volcanic indurated soils called tepetates in Mexico must control soil erosion and generate a good productivity of these new soils according to a sustainable development strategy. This paper shows the results of an european research program involving ORSTOM and the Colegio de Postgraduados en Agrociencas in the eastearn part of the valley of Mexico (Texcoco). Different systems of culture have been studied (mono/associated culture, with/without manure, soil/tepetate, natural/cultivated tepetate, tepetate with deep/normal subsoiling, tillage practice) during four years on a 8 large terraces (700 m 2 ). After every rain, we measured the runoff, took and dried all the sediments, sampled water and followed the vegetation cover, the soil surface aggregates, the crops growing (see this papers in this publication). In the study area, only few events generated an important soil erosion: 16 events ≥10 mm, representing 50% of the total volume of the rain and 80% of the R us of the year. Only 3 events had an energy >500 MJ/ha. For all the rain ≥1 mm, this R us varied beetwen 55 and 150. So it is not the annual R which is important but the frequency and the intensity of the rain during the year. In fact the annual and daily difference had more impact on the runoff and erosion than the kind of soils, crops and soil practices. On the natural tepetate, 75% of the rain runoff and the runoff coefficient (Kr) is between 40 and 50%. The soil erosion varies from 10 to 30 t/ha/year, with an average of 20 t/ha/year. The solid charge is 30%, showing that the erosion is more a gully than a laminar erosion. This is the consequence of the indurationof the material which provokes high ranges of runoff. Water concentrates along the slope, and with the energy accumulated, is able to generate a deep and catastrophic soil erosion on the lower part of the hills, as it is possible to see on the actual landscape. In spite of the fact that the reclamation of the tepetate was controlled and the terraces were on the same area, we noticed differences in the results due to the station. So, we distinguish 2 groups, the upper and the lower terraces, and we still study the reasons of these differences. For the upper terraces, in the case of barley, during a dry year, the Kr is under 15% and the E=1 to 6 t/ha/year meanwhile in a rainy year, the Kr is 50% and the E between 10 to 30 t/ha/year. In the case of corn growing on the same terraces, during a rainy year, the Kr is around 30% and the E=4 to 15 t/ha/year. For the lower terraces, in the case of the barley, during a dry year, the Kr is under 5% and the E is 1 t/ha/year. In the case of the corn growing on the same terraces during a rainy year, the Kr is around 10% and the E is less than 1.5 t/ha/year. Barley reduces less and generates more soil loss than corn. But, in this case, the raw and the work of cleaning the fields must be made with care and at the good moment. Thie raw with little rain catchment is a very good alternative with this climate because it strongly reduces soil erosion and the production of string beans is higher (meanwhile there is no effect on corn production). The association of string beans and corn reduces soil erosion and increases the productivity of both cultures in relation with the monoculture.