| Popis: |
"In the past centuries man incorporated many fragile natural resources into production in Mexico and Central America and exploited them under low intensity slash-and-burn system preserving their integrity for long periods. However, in more recent times, such agro-ecosystems have been subjected to over exploitation and intensive use, in terms of time and space, without consideration for their lack of resilience, due to population growth and the demands to generate profits, as established by the prevailing economic model. The standing practices have resulted in severe human induced land degradation, particularly in tropical areas. Land degradation in desert areas is more a natural type of degradation than an anthropogenic one. A series of alternative technologies to reduce the impact of human activities have been proposed in recent years. Among them, different types of alternative agriculture oriented either to regenerate some of the properties of the systems or to reach its stability. Conservation tillage is an example. Other, is intercropping staple crops and fruit trees (MIAF) techniques developed for hillside agriculture (20 to 60 % slopes) in Mexico. Conservation tillage and MIAF are intimately related to carbon sequestration (soils and above-ground) and to preventing soi1 erosion. It has been shown in Mexico that the rate of carbon entrance to these systems exceeds the rate of carbon exit. The root residues left in the soi1 contribute after decomposition to the soi1 carbon reservoirs, however, the quantity of carbon remaining in the soi1 after a time is dependent on and controlled by the own system. In contrast, above-ground residues, which are also controlled by the system, may or may not become part of the carbon reserve of the soi1 because man as an external agent decides the final destination of this carbon. The identification and understanding the structure of the system, and its components, as well as, the role that each of these components plays, is fundamental to intervene in the system and decide on the most appropriate direction. Efforts have been made lately in Mexico and Central America to benefit from international agreements that have created an emerging market for the sequestered carbon. The conservation tillage is one of the agronomie practices linked to preserving soi1 carbon and even to increasing it, however, a limited surface is maintained under this system in Mexico and Central America, as compared to Argentina and Brazil. A scarce availability of technology for the mostly tropical and hillside agriculture conditions in these regions of the world is often blamed for such situation. However, on-going-research efforts to better understand and to practice conservation agriculture leading to decrease soi1 erosion and increase carbon sequestration are rather limited." |
