Adubação orgânica de alface: contaminação microbiológica e desenvolvimento da cultura, aspectos químicos e biológicos do solo

Abstract

The lettuce (Lactuca sativa L.) in Brazil is one of the most significant crop in economic importance and as food stands out among the leafy vegetables most consumed. The conventional production system uses chemical fertilizers as nutrient source for plants, which may cause risks to human health because of its toxicity, and represents a significant cost to the producer. An alternative is the use of organic compounds obtained via composting and vermicomposting. However, poor process conduction of composting and vermicomposting may result in no elimination of pathogens present in the waste source. Furthermore, the bad fertilizer storage conditions may cause contamination by feces vectors. In this sense, the objective was to evaluate the effects of organic fertilization in lettuce cultivation in microbiological quality and culture development, as well as in chemical and biological aspects of the soil. It was evaluated: contamination of lettuce and fertilizers by Salmonella sp and Escherichia coli; development of lettuce; macro and micro nutrients in fertilizers (pre-plant) and in soil (after planting); organic carbon and microbial soil respiration. The cultivation was carried out for 40 days considering the use of compounds (C) and vermicompost (V) from different waste: T0- soil (witness); T1- horse manure + coffee straw (C); T2- horse manure + sawdust + brachiaria (C); T3- horse manure + rice husk (C); T4- horse manure + rice husk + brachiaria (C); T5- dairy sludge + tree pruning (C); T6- dairy sludge + pruning tree + boiler ash (C); T7- dairy sludge + tree pruning (V); T8- dairy sludge + pruning tree + boiler ash (V); T9- NPK. At the end of this experiment it can be observed that the development of lettuce plants is affected directly by the various sources of nutrients, and fertilizers based in equine manure were more effective in the development of lettuce. T4 showed similar results concerning to T9 proving that use of organic compound as a way of nutrient supply can be done instead of chemical fertilizers. T0 showed low development of culture, indicating the need of adding nutritional sources in the soil. Despite the contamination by fecal coliforms in T4, T5 and T8 before planting, there was no occurrence of lettuce contamination by Salmonella sp and Escherichia coli. There was an increase in the levels of organic carbon and macro and micronutrients in soil; microbial soil respiration presented independent behavior of the composition of fertilizers.