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.

Adubação nitrogenada no milho em sucessão à plantas de cobertura sob sistemas de cultivo do solo

To achieve high yields the corn crop is dependent on nitrogen. Systems of cover crops preceding corn and form of land cultivation are essential for the best use of nitrogen by corn. This study aimed to evaluate the use or not of nitrogen fertilization in corn in succession to cover crops, planted in three cropping systems. The experimental design was randomized blocks with sub-divided portion where the main plots consisted of three cultivation systems (tillage, conventional tillage and minimum tillage), the subplots by four plant cover in monocrop (oat, hairy vetch, field peas and turnip) and sub-subplots by nitrogen fertilization (0 and 160 kg ha-1 N). Evaluations were performed, the cover crops, soil cover rate, dry matter, content and accumulation of nutrients. In corn we evaluated yield components, yield, chlorophyll and nutrient levels in leaves. Among the species coverage studied the oat showed hardiness in the experiment, covering ground faster and showing more dry matter, however vetch hairy showed higher concentrations of N, P and K and higher accumulation of N ha-1. The soil tillage system influenced the K leaf content. The interaction cultivation x coverage showed significance for the total chlorophyll of corn. In the absence of N, N content and chlorophyll were higher where the corn was sown on the pea and hairy vetch. The corn production, despite a higher average in the presence of nitrogen fertilization, did not differ significantly when used the pea and hairy vetch as a cover crop.

Controle social e políticas públicas: contribuições para aprimorar o controle social do programa nacional de alimentação escolar

The National School Feeding Programme (PNAE) is a public policy in Brazil for over 60 years and represents one of the most important programs of feeding and nutrition in the world. The role of family farming as a source of employment in rural areas, food provider and for ensuring much of the Brazil’s food security is constantly present at the government's and social movement’s agendas. Law 11.947 of 2009 marked its integration in the food supply for the National School Feeding Programme. Article 14 of aforementioned law highlights that a minimum of 30% (thirty percent) of the funds transferred by the National Development Fund Education (FNDE) to the Programme must be used for the purchase of food directly from family farmers or their organizations. The national school feeding policy under the responsibility of the FNDE and is subjected to agencies of internal control, such as the General Controllership of the Union (CGU), of external control, such as the Audit Courts of the Union and the of the states, and to the social control of the school feeding councils. Those funds are transferred to the implementing agencies, which are the education offices of the states, municipalities and of the Federal District. These entities must annually present their accountings to the School Feeding Councils, which analyze them and then issue a conclusive report to the FNDE, approving with or without reservations, or rejecting them. In this sense, this research aims to propose parameters that should contribute to the improvement of the social control over purchases from family farming for the National School Feeding Programme. The study was conducted by non parametric sampling alongside the managers of the implementing entities, school feeding councils and Family Farming Organizations all across Brazil, from the databases provided by FNDE and by the National Union of Cooperatives of Family Agriculture and Solidarity Economy (Unicafes). The study points out that the legal framework of PNAE seeks to ensure the participation of family farming in the food supply for the Programme, despite allowing the executing agencies to justify the non-compliance of the minimum required in a number of ways. The survey also signalizes that the school feeding councils follow the implementation of the Programme very shyly, and points out that there is room to expand and enhance the participation of these councils and organizations of family farming in the execution of PNAE. Its effectiveness requires a constant and effective process of training of the agents involved in the Programme.