Destino no ambiente e comportamento agronômico de atrazina em resposta a doses e níveis de palha de espécies de cobertura de solo

The use of cover crops is a fundamental strategy to the weed management in Southern Brazil. In highly infested areas, the herbicides use is increasing, which increases the costs of the crops production as well as the environmental contamination. Oat and velvet bean plants havecontrasting characteristics regarding to residues decomposition speed and the capacity to immobilize Nitrogen in the soil, providing distinct results of weeds suppression throughout the time, and therefore, requiring distinct management strategies before, during, and after the corn crop establishment. The general objective of the experiment was to evaluate the environmental dynamics of the herbicide atrazine, the corn grain yield, and the efficiency of the weed control, considering areas with distinct history regarding the use of mulching, levels of straw and rates of atrazine. For this, the experiment was carried out in two parts: in the first part, two trials with the corn crop were established, one using oat and the other using velvet bean as cover crops. The experimental design used for both field trials was randomized complete blocks arrangement with four replications. The factor A was constituted by four levels of straw (0; 0.75x; 1.5x; 3x) and the factor B was constituted by four rates of the herbicide atrazine (0; 2100; 4200; 8400 g a i. ha-1). Soil samples were collected for greenhouse trialsto determine the persistence. Atrazine leaching evaluation was performed by chromatography using samples collected over the soil profile.In the field, the weed density, the fresh and dry weight and the yield of the corn were evaluated. In the greenhouse trials, the main variables evaluated were plant height and injury caused by the herbicide toxicity. In the second part, soils with distinct covering history were sampled, and the mineralization and sorption studies, both with 14C-atrazine, were conducted in the laboratory. The experimental design was randomized complete blocks arrangement with four replications. The results from the field experiment show that the high levels of straw above ground, isolated, were not efficient to control completely the weeds, and that high levels of velvet bean`s straw decreased the corn potential yield. The greenhouse trials showed that high levels of oat straw prevent the scape of atrazine to soil, this effect of oat straw upon the herbicide availability on soil was detected up to 12 days after spraying. The half-life of atrazine sprayed over oat straw varied from 7 to 14 days after spraying, while the half-life of atrazine sprayed over velvet bean varied from 5 to 14 days after spraying. Increasing oat straw levels presents the capacity to reduce the lixiviation of atrazine in the soil profile, however, this effect was not verified when using velvet bean straw, because the herbicide was not detected in the soil profile, at 21 days after spraying. The chromatographic analysis indicate thatthe atrazine concentrates closer to the soil surface regardless of amount of straw, not being detected deeper than 8 cm in the soil. The accumulated mineralization of 14C-arazine sprayed over V. sativa is superior if compared to soils with S. cereale or non-covered soils. The sorption coefficient of atrazine is superior when sprayed over straw than over the soil.

Estudo de caso: minimização e reúso de água em shopping center da região sul do Brasil

The main issues related to water conservation in urban centers are the increase in water supply cost, demand growth, pollution and differences in the distribution of water resources. Water conservation, the controlled and efficient use of water, includes both measures as reasonable means of water reuse. Thus, conservation practices are an effective way to meet demand and supply water to new activities and users without jeopardizing the supplying water bodies and preserving the natural environment. This study aims to examine the water management of a shopping mall and the use of rainwater harvesting combined with greywater reuse. For buildings in general, water loss is common due to leaks in the hydraulic and restroom equipment. These losses, which are caused by a high volume of water used and wasted in the system, are often the result of design errors, incorrect maintenance procedures and users' bad habits In southern Brazil, where there is rainfall almost all year long, water shortages occasionally occur, particularly in some winter mouths. One difficulty that appears on rainwater studies is the proper determination of rainwater volume that can be used to address water supply systems. In this work, the simulation method was used to determine this volume. Thus, simulations with the following variables: rainfall, catchment area and water consumption were performed. For mall's hydraulic systems, segmented alternatives are adopted. That is, focusing on the use of rainwater or greywater reuse. Other alternatives of effluent reuse have been slightly discussed due to sanitary issues, those are effluents from toilets and kitchen sinks. The adoption of greywater may be feasible if there is a significant flow of greywater to comply water demand for toilet flushing. The inspections made in this study found that the quantity of sinks was insufficient to supply an adequate amount of water to toilets and urinals. The greywater reuse system was found to be infeasible in terms of demand and supply of water. Conversely, the rainwater harvesting system was entirely feasible and easily supplied water to all restrooms and contributed to the cooling of the air conditioning system with a short payback period. One of the challenges of this work was the need to compare the actual water consumption with a water consumption parameter used in buildings. Thus, a method that addresses the generation of specific consumption indexes for specific activity (like a mall) was used. The water consumption indices showed that this mall has a satisfactory water management program.