Introduction At the beginning of the twentieth century, agricultural products provided food to a world population of about 1200 million people, whereas nowadays they do for a population of about 6000 million. Due to the increasing population growth rate which is about 60 million people/year by 2020 the population will be around 8000 million. Some projections indicate that by then the world production of the main crops will have to be increased by about 700 million tons. The speed of these changes leads to the need to pay attention to the consequences brought about by this demand, such as the massive use of agrochemicals, which, in turn do not allow the maintenance of soil productivity.