Alterações na matéria orgânica e na biomassa microbiana em solo de mata natural submetido a diferentes manejos Changes in organic matter and in microbial biomass of a natural forest soil under different management

Avaliou-se, em um Latossolo Roxo, o efeito de diferentes formas de manejo do solo sobre a matéria orgânica do solo e na biomassa microbiana. Os tratamentos usados foram: mata natural; mata natural até 1976 e café até 1994 (amostragem na projeção da copa e na entrelinha); mata natural até 1976, café até 1991 e milho até 1994; mata natural até 1940, café até 1960, citros até 1978, e cana-de-açúcar até 1994 (amostragem na linha e na entrelinha). A mata natural apresentou os maiores valores de C orgânico no solo e na fração humina e os menores valores foram obtidos nas áreas com cana-de-açúcar, que apresentaram os maiores valores de C microbiano em relação à mata natural. O uso agrícola do solo aumentou a porcentagem de C orgânico na forma de ácidos húmicos e fúlvicos, em relação à mata natural. Em geral, o solo apresentou mais de 74% do C orgânico na forma de húmus residual.<br>The effect of soil management on forms of carbon and microbial biomass was studied in a Typic Euthortox soil. The treatments tested were: natural forest; natural forest till 1976 and coffee till 1994 (sampling on the shoot projection and between lines ); natural forest till 1976, coffee till 1991 and corn till 1994; natural forest till 1940, coffee till 1960, citrus till 1978 and sugar cane till 1994 (sampling on the planting line and between lines ). The treatment with sugar cane presented the largest values of microbial carbon in relation to the natural forest. The agricultural management of soil increased the percentage of organic carbon in humic and fulvic acids forms. The soil presented more than 74% of organic carbon in the form of residual humus

Applications of Fertilizer Cations Affect Cadmium and Zinc Concentrations in Soil Solutions and Uptake by Plants

A pot experiment was conducted to study changes over time of Cd and Zn in soil solution and in plants. Radish was grown in a soil which had been contaminated with heavy metals prior to 1961. Constant amounts of a fertilizer solution (NH4NO3, KNO3) were added daily. Soil solution was obtained at intervals by displacement with water. The cumulative additions of small amounts of fertilizers were made equal to the plants' requirements at the final harvest but were found to exceed them during most of the experiment. Excess fertilizers caused substantial increases of major (K, Ca, Mg) and heavy-metal (Cd, Zn) ions in soil solutions and a decrease in soil pH, probably due to ion-exchange mechanisms and the dissolution of carbonates. Uptake of Cd and Zn into leaves was correlated with the mass flow of Cd (adjusted r = 0.798) and Zn (adjusted r2 = 0.859). Uptake of K, Ca and Mg by the plants was independent of their concentrations in solution. It is concluded that, in order to study effects of plants on heavy-metal availability and obtain soil solution that has not been altered by fertilizer ions, nutrients must be added according to the needs and growth of the plants. This could be achieved by linking fertilizer additions to the rate of transpiration, as nutrient uptake and transpiration were closely correlated in this experiment