Nutrients in soil solution in an upland forest submitted to selective logging in central Amazonia

Abstract

The nutrients NO 3 -, NH 4 +, K +, Ca 2+, Mg 2+ and Na + were determined in a soil solution in a layer 0-30 cm, in an area submitted to selective logging (6-10 trees or 34 m 3 ha -1 of timber), located 80 km north of Manaus. The experiment was made up of three blocks, each containing one control plot and one plot submitted to selective logging. The soil in the area is very clayey Alic Yellow Latosol, with a high clay content. The samples were collected and analysed during 13 months in five treatments: control (pristine forest), centre of the clear-cut, edge of the clear-cut, edge of the remaining forest and remaining forest. Calcium, magnesium, potassium and sodium concentrations showed significant differences among the different treatment. Nitrate and ammonium ions were the less affected concentrations. In the treatments centre of the clear-cut and edge of the clear-cut, the nutrient results were, mostly, the highest values. The greatest difference occurred in the sodium concentration in the soil solution, which reached 5 kg/ha, in the centre of clear-cut of Blocks I and II, being practically twice as much as the values found on their respective control plots. The lowest concentrations of the nutrients in the soil solution on the pristine forest (control plot) and in the remaining forest confirm the efficiency of the forest in nutrient cycling. The higher concentration values of these nutrients in the centre of the clearcut, might be possibly due to the removal of trees, availability of easily decomposable materials like dead roots and accumulated litter.