Rationality in the Use of Non Renewable Natural Resources in Agriculture

Abstract

The increase in human population and the demand for life quality have induced the growing production of food and alternative vegetal energy sources in replacement to petrol. Soybean responds to more than 80% of biodiesel production, and will reach 5% inclusion in the fossil diesel in the next years in Brazil. This trend will increase pressure to new areas for soybean production on actually human food production areas, as well on pasture and untouched forests areas. The progress of agriculture has been based on increase in animals and plants productivity per unit of area, which only has application when land availability is the sole limiting factor. However, the efficiency of use of limiting resources (including water, fertilizers and petrol) has to be considered. This mistaken vision is leading to excessive use of non renewable natural resources and environmental pollution. The reserves of phosphate in the world that can be explored at low cost are enough for 40 to 100 years and the world reserves of potassium are enough for 50 to 200 years. The situation is worse for micronutrients, in which the reserves of copper and zinc are enough for 60 years, manganese for 35 years and selenium for 55 years (Herring & Fantel, 1993; Roberts & Stewart, 2002; Aaron, 2005). In addition to the depletion of natural reserves, the excessive use of fertilizers can contribute to soil and water courses contamination with nitrate (Angus, 1995; Bumb, 1995), soil acidification (Helyar & Poter, 1989), and emissions of carbon dioxide (CO2), nitrous oxide (N2O) and ammonia to the atmosphere. The pollution with nitrate has being an actual preoccupation in Europe and North America. The fertilization with phosphorus and nitrogen cause decrease in water oxygenation by excessive increase in the population of toxic algae in the oceans (Kebreab et al., 2002). The agriculture participates in 20% of annual increase in the anthropogenic emission of greenhouse gases, mainly CH4 and N2O. Approximately 70% of all anthropogenic emission of N2O is attributed to agriculture. The current methodology used in Canada to estimate the flow of N2O is based in the direct relation between the emission of N2O and the application of nitrogen fertilizers (Lemke et al., 1998). The possible deleterious effects of emissions of N2O are global warming and catalytic destruction of the ozone chain in the stratosphere, in which the N2O retains 13 times more heat than methane (CH4) and 270 times more than CO2 (Granli & Bockman, 1994). The atmospheric level of N2O has increased in growing fashion since 1960, associated with increase in utilization of nitrogen fertilizers (Bumb, 1995; Strong, 1995).