Rafael Silva Guedes

Impacts of different management systems on the physical quality of an Amazonian Oxisol

The physical quality of Amazonian soils is relatively unexplored, due to the unique characteristics of these soils. The index of soil physical quality is a widely accepted measure of the structural quality of soils and has been used to specify the structural quality of some tropical soils, as for example of the Cerrado ecoregion of Brazil. The research objective was to evaluate the physical quality index of an Amazonian dystrophic Oxisol under different management systems. Soils under five managements were sampled in Paragominas, State of Para: 1) a 20-year-old second-growth forest (Forest); 2) Brachiaria sp pasture; 3) four years of no-tillage (NT4.); 4) eight years of no-tillage (NT8); and 5) two years of conventional tillage (CT2). The soil samples were evaluated for bulk density, macro and microporosity and for soil water retention. The physical quality index of the samples was calculated and the resulting value correlated with soil organic matter, bulk density and porosity. The surface layers of all systems were more compacted than those of the forest. The physical quality of the soil was best represented by the relations of the S index to bulk density and soil organic matter.

Maximum Phosphorus Adsorption Capacity Adjusted to Isotherm Models in Representative Soils of Eastern Amazon

Most soils of the Amazon present low natural fertility and may also present high phosphorus (P)–fixation capacity. Clay fraction mineralogy, organic carbon, cation exchange capacity (CEC), and pH are among the factors that influence P adsorption. In this study, we aimed to evaluate the maximum P-adsorption capacity (MPAC) and correlate parameters of the isotherm models and the MPAC with soil attributes. Soil samples were collected in 12 forest soils in the state of Pará. We built Langmuir and Freundlich isotherms, and their parameters correlated with soil attributes. MPAC was greater in Plinthosols, among the soils studied at both depths. In superficial soil layers, the parameters of Langmuir-Freundlich equations correlated with clay content, pH, organic matter (OM), aluminum oxide (Al2O3), and iron oxide (Fe2O3) at both depths. The Langmuir model is more representative of the adsorption of P relative to the Freundlich model for the Amazon region soils, where it is necessary to make use of organic matter and pH control as a means of reducing the retention and P and maximize the effects of fertilization phosphate.

Effect of waste mixed with biochar as soil amendment on trace element solubility in a mine soil

Abandoned mining sites often cause contamination of surface and subsurface waters. A 3-month pot experiment was performed to evaluate the influence of waste mixed with biochar as a soil amendment on a series of chemical characteristics and trace element solubility in a mine soil. Trace element concentrations were measured in pore water of the mine soil reclaimed with different proportions of waste-biochar amendment (20, 40, 80 and 100%) and grown with Brassica juncea. The results showed that amendment application improved soil conditions such as pH, total carbon, dissolved organic carbon, total nitrogen, and strongly reduced the concentration of Al (99.99%), Co (99.95%), Cu (99.97%), Fe (99.79%) and Ni (99.91%) in pore water, compared to the unamended soils. Waste and biochar also promoted the establishment of B. juncea in the mine soil. These results highlight the importance of mitigating the impacts from abandoned mines sites on water quality. The use of waste and biochar as soil amendment combined with B. juncea plants was effective in reducing metal concentrations in pore water and the associated toxicity risk.