The society has been increasingly concerned about environmental damage caused by agricultural activities, especially with regard to health hazards resulting from the use of agrochemicals. On the other hand, growing phytosanitary problems and ever-increasingly depauperate soils lead to an all time high utilization of these products. Sustainability of conventional agriculture started being questioned, and the agricultural scene experienced changes (Van Bruggen, 1995). The emergence of market segments interested in differentiated products lead farmers to search for alternative cropping systems, enabling the production of food crops at lower environmental and economic costs.
Many alternative cropping systems have been developed and, among them, organic agriculture has been established and certified in many countries. Organic agriculture is characterized by the absence of synthetic fertilizers and pesticides, in addition to the frequent utilization of organic matter sources to maintain soil fertility (Stanhill, 1990; Van Bruggen, 1995).
The adoption of the new practices brought, however, the need for comparison between low-input against conventional systems. In addition, recovering the principles and mechanisms that operate in the nature to be utilized as replacement for the traditional input, will only be achieved if a broad base of knowledge of the complex relationships between organisms and their relationship with the environment is available (Edwards, 1989; Ghini & Bettiol, 2000). To that effect, interdisciplinary studies are needed to verify whether or not the sustainability of the agroecosystems can be achieved. Although the development of ecologically sound agriculture systems is rapidly emerging as a priority, few research papers have detailed the effects and interactions of the new proposed practices.
Tomato cropping is an excellent model for comparisons between the conventional and the organic systems for reasons like the intense use of agricultural input and the risk of contamination of consumers, farmers and ground water by agrochemicals (Drinkwater et al., 1995). In an interdisciplinary study, Drinkwater et al. (1995) evaluated several agronomical and ecological indicators in the organic and conventional tomato cropping systems in California (USA), and concluded that biotic agents are essential to make up for the absence of synthetic input. However, the involved mechanisms are much more complex than a mere replacement. For example, soil fertility management practices affected C and N dynamics and, as a consequence, also affected pathogen-host relationships and plant-herbivores interactions through community level mechanisms.
Creamer et al. (1996) compared in two locations the conventional, integrated, organic and no-input systems tomato cropping systems; the last three systems were associated to a cover crop. The number of fruits and flower clusters were higher in the conventional system during the initial assessments, becoming equivalent to the other systems later. No differences were observed with regard to the occurrence of pests and diseases among the treatments. In one of the regions, there was greater accumulation of plant dry matter and higher tomato yield in the conventional system than in other treatments, which represented greater economic gain. In the other region, however, no differences were observed among the systems. The differences between regions were associated with soil type and climate and, demonstrated the need for more studies to be carried out under different conditions.
The objective of this work was to compare organic and conventional tomato cropping systems, by evaluating plant development, occurrence of diseases and weeds, microorganisms and arthropods in the phyllosphere, and tomato yield.