Seleção de milho para tolerância a alumínio.

Solos acidos sao frequentemente em areas tropicais do mundo. Os solos que mais atingem a adaptacao de plantas nessas regioes sao os Oxisolos, que ocupam 8,11% das terras do planeta. Sao solos muito intemperizados e tem baixa capacidade de troca de cations. E comum apresentarem deficiencia de Ca e Mg, presenca de aluminio trocavel e possibilidade de fixacao de fosfatos em minerais como sesquioxidos. Uma alta saturacao de aluminio no solo e toxico para o desenvolvimento de plantas. Aluminio afeta muitos processos fisiologicos, bioquimicos e metabolicos da planta e pode causar injurias as raizes. Metodologia de solucao nutritiva e teste no campo tem sido desenvolvidas para uso em melhoramento. Ja foi dectada variabilidade para tolerancia a aluminio em milho e tolerancia a aluminio tem sido desenvolvidos e a tolerancia tem sido adicionada a genotipos de alta produtividade e estaveis. Estuda-se tambem a associacao de tolerancia a aluminio com eficiencia de fosforo em solos acidos

Influência da adubação fosfatada e calagem sobre a absorção do zinco, em dois solos de Minas.

Two experiments were installed in the greenhouse to study the relationships between phosphate fertilization, liming and zinc fertilization. One experiment used a red latosol soil while the other used a dark brown acid soil. Hybrid corn AG 206 was used to plant both experiments. The data collected consisted of dry matter productions level of zinc in the leaves, stems and tootes of the corn as well as the P/Zn and Ca/Zn rations in the leaves. Phosphate fertilization and liming lowed the level of zinc in the corn leaves to a point equal to or lower than 14 ppm. These leves were below 80% of the maximum yields of the experiments. The application of 4,5 ppm of zinc to the soil was adequate to raise the level of zinc in the leaves above the critical level. It also increase the production was limited by a zinc deficiency. The phosphorus and zinc interaction, which ocurred primarily in the roots of the plant, reduced the translocation of zinc to the leaves. The interaction between liming and zinc ocurred prior to the absorption of zinc by the plant. It aprears that there are ratios between phosphorus and zinc between calcium and zinc in the leaves which are critical to good plant growth. The critical P/Zn ratio is betwee 300 and 470 and the critical Ca/Zn ratio between 455-640

Soil quality and agricultural sustainability in the Brazilian Cerrado.

The "Cerrado Region" - the acid savannas of Brazil, as many as thirty years ago, were considered as ecosystem unsuitable for agriculture crop production because environmental limitations. However, a burst in agricultural development has taken place in the area during last decades as a result of new technology mainly involving plant breeding and soil management. In spite of the great contribution made by the "Cerrado" region to the Brazilian agricultural production, over the past few years concerns have been raised about the issue of the high costs of this agriculture production and about the issue of soil quality degradation, and how it could affect the sustainability of the agriculture in the "Cerrado" ecosystem. The concept of sustainable agriculture is well recognized research, development, and productive segments of today's agriculture, however, the notion of how to measure and monitor sustainability of farming systems is much les understood. This paper proposes a system of measuring and monitoring the sustainability of farming systems using soil quality indicators in the acid savannas of Brazil. The methodology utilized and agroecological framework to examine the relations among natural resources and agriculture, selectiong one agroecological zone inserted in the cerrado ecosystem. This selected zone was subdivided into regions superimposing Census data, because policy and socioeconomic differences among regions have a considerable influence on land-use systems and options. Target areas were selected and participatory rural appraisal procedure was used to supplement voids in data, identify and characterize predominant farming systems, and to capture farmer knowledge. Using this farmer knowledge, research results already available and local observations, the mainly factors affecting soil quality were identified. Assuming that a management system is sustainable only when soil quality is maintained of improved, physical, chemical and biological properties, processes and characteristics were closen as indicators to make qualitative and quantitative assessment of the changes in soil quality. Based upon these evaluations, a general procedure or framework for sustainability assessment was developed. Using the procedure, it is possible to identify whether current management interventions are contributing towards or away from sustainable farming management, and to develop strategies to improve sustainability of those systems