Improvement of the soil fertility of a volcanic indurate layer (Tepetate) by applying acid treated biosolids
Volcanic indurate matter produces low soil fertility when rises to the surface, reducing the agricultural potential of the land and distressing marginal zones that live from agriculture. The habilitation of these materials using biosolids has not been explored, although the problem exists in several countries around the world. This work evaluated the impact of the application of biosolids on the fertility of a fragmented volcanic indurate layer (Tepetate). Tepetate’s fertility was measured before and after biosolids application with three biosolids application rates: agronomic rate (AR), as well as 10 and 20xAR. Biosolids were mixed with Tepetate and kept in pots under green house conditions along with a control, during four months. One set of pots with and without vegetative species. Organic matter content increased between 180 and 470% compared to the control. Cation exchange capacity (21.8 to 42.3 Cmol+kg-) resulted adequate for keeping nutrients for plants. pH values were adequate for agricultural activities (5.9-7.2). Dry color of the Tepetate, becomes darker (grayish brown; 10YR 5/2) than the initial yellowish brown (10YR 5/4) because of the addition of stable organic matter from biosolids. Considering edaphologic characteristics it is suitable to habilitate volcanic indurate layer by the application of biosolids.
Tepetates of Central Mexico : paleogeographical background and functioning in modern agroecosystems
Volcanic soils with indurate subsurface horizons (having the local name tepetates), totally or partly cemented by silica, 1:1 clays, and iron oxides or calcium carbonates, cover about 660,000 km. In a number of earlier works, focused on identification of cementing agents and ecological significance of tepetates, they were considered as pedogenic phenomena; however, though they are often inter-layered with or overlain by paleosols, they were never related to the past soil forming processes and environmental conditions. We studied spatial distribution and properties of tepetates, associated soils and paleosols in Morelos State/ Central Mexico to understand the (paleo) environmental conditions and processes of their formation which pre-determinate their specific impact on the functioning of agroecosystems. In the key site of the Glacis de Buenavista, tepetates are overlain with thick profiles of welded Luvisols of the Late PleistoceneHolocene age. The Luvisol Bt horizons are characterized by extensive 1:1 clay accumulation due to in situ weathering and clay illuviation, high content of free iron oxides, and redoximorphic pedofeatures. All these properties indicate long-term pedogenesis under humid forest environments. Underlying tepetates have lower clay and free iron content. In tepetates thin sections, we observed a peculiar combination of the re-deposited material of Luvisol Bt horizons and fragments of fresh volcanogenic rocks and minerals. Materials, typical for the surface soil horizons – phytoliths and small charcoal fragments – were also found. Besides re-deposited illuvial pedofeatures, there are in situ clay coatings and infillings as well as ferruginous mottles and nodules. We interpret the observed combination of properties in the Luvisols and tepetates as result of interaction of long-term humid pedogenesis and regular catastrophic volcanic events. The period between eruptions was long enough for formation of Luvisols with Bt horizon rich in crystalline 1:1 clay. Association of re-deposited material of different soil horizons and fresh volcanic components in tepetates suppose that they are formed by mass movement processes, linked to eruptions: lahars and mud flows. The sediment, thus formed, contains sand and silt, mostly of volcanic origin, and clay from soil material, in proportions that are favourable for its structural collapse and hydroconsolidation when moistened and loaded. Further clay illuviation and redoximorphic segregation of iron oxides filled few pores left after primary consolidation, and thus contributed to tepetate induration. Presence of subsurface indurate horizons with low permeability promotes lateral soil drainage and could provoke erosion. Such Luvisol-Tepetate profiles are stable in the natural ecosystems, SOLLEIRO-REBOLLEDO ET AL. 17 WCSS, 14-21 August 2002, Thailand 1914-2 were dense forest vegetation prevents soil losses with runoff. Under cultivation the accelerated erosion could destroy quickly the upper part of the profile, exposing tepetates to the surface and causing advanced land degradation. High density that hampers root penetration and provokes strong surface runoff, very limited water availability and low cation exchange capacity cause the drop of agroecosystem productivity. Vast areas covered by tepetates are set aside as badlands.
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.