Análise multidimensional das pressões dos sistemas de produção agrícola na Bacia Hidrográfica do Rio Guaporé (Brasil/RS)

Abstract

Agricultural activities developed to meet human needs exert stress on the environment, so quantifying them is a complex task. In this way, the aim of this research is to analyze the pressures of family agricultural production systems on water dynamics in the Guaporé River Basin (RS). For this, based on documentary, bibliographic and field research, and with information collected from local actors and experts in the area of water resources and river basin management, a multidimensional evaluation model was structured that combines seven criteria and 25 sub-criteria for two major areas: (i) land occupation and soil management and (ii) agricultural waste. The model was tested in 14 family farms, which represent the four productive arrangements developed in the watershed: grain production system, conventional crops, animal integration and perennial farms. The results show that, although the production systems developed have evolved and adapted to the new technical and socioeconomic environments, they occupy ecologically fragile environments, in particular as regards the use of land with low agricultural aptitude, and are often carried out with no conservationist practices and inadequate management of natural resources. Based on the elaborated model, tobacco cultivation, chosen to represent conventional crops, demonstrates greater negative interference in aquatic systems. This performance is a consequence of the constant removal of soils (shallow and with high erodibility potential) located on the slopes (generally with a slope above 16 degrees) associated with the reduced adoption of conservationist practices. In contrast, the system of perennial farms, evaluated under the cultivation of yerba mate (Ilex paraguariensis), expressed the best results for maintenance of water resources. Land use adjustments can make this system even less harmful to the environment. Between these two systems are the performance of rainfed grain crops and animal husbandry. The first of these, portrayed by soy cultivation, occupies the region with natural environmental and soil characteristics favorable for agricultural crops, however, the exacerbated consumption of pesticides compromises the performance of the system. In the system involving the raising of pigs and cattle, the continuous use of high doses of animal waste, which increases the propensity to transfer pollutants to the water bodies, justifies the negative performance in relation to the evaluation model used. It is important to communicate that this is an initial assessment, so from a methodological perspective, research signals a starting point for studies interested in environmental indicators for agricultural activities.