Monoammonium phosphate (MAP), triple superphosphate (TSP), and phosphoric acid (H3PO4), with and without the addition of magnesium oxide (MgO), were mixed with poultry litter (PL) to produce biochar-based fertilizers (BBFs). This is a novel approach aiming to add value to PL residue and to increase P use efficiency in acidic tropical soils. Samples of BBFs were assessed by P-release kinetics in water, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and a bioassay with maize in a greenhouse using a clayey Oxisol. Addition of MgO reduced the kinetics of P released from BBFs impregnated with all P sources. XRD analysis showed the formation of low-solubility Ca2P2O7 and Mg2P207 compounds, which is supported by POP or PO stretching observed in the FTIR spectra. The MgO-treated BBFs increased shoot dry matter production compared to the control, but were inferior when compared to TSP in the short term. The slow release of P and the alkaline reaction of the BBFs show great potential for these materials to be used as enhanced P fertilizers in tropical soils.

Aim Soil incorporation of Si-rich rice residues may aid smallholder rice farmers in improving crop yields and may affect As uptake. Here, the biogeochemical impacts of rice residue incorporation into flooded soil without plants were evaluated. Methods Various particle sizes of fresh rice straw (FS), fresh rice husk (FH), rice straw ash (RSA) and rice husk ash (RHA) residues were incorporated into soil (1 % w/w) in a flooded pot experiment. Pore-water chemistry was monitored weekly and dissolved CH 4 concentrations and genes specific for methanotrophy and methanogenesis in DNA extracts of soil were evaluated. Results FH-amended soil had the highest level of dissolved Si, followed by FS and then ash (RHA or RSA). Particle size had little effect on the dissolved Si concentration for any residue tested. No amendments had any substantial effect on pore-water pH. FS-amended soil had much higher As, Fe, and CH 4 concentrations in pore-water compared to ash and FH, and its extracted DNA also had higher amplifications of genes indicative of methanogenesis. Conclusion FH, RHA, or RSA are attractive amendments for smallholder rice farmers to increase plantavailable Si without exacerbating CH 4 emissions, which may improve rice nutrition through the beneficial impacts of Si on combating biotic and abiotic stress including decreased arsenic uptake.

No abstract

No abstract

High concentrations of total arsenic (As) have been measured in soils of gold mining areas of Brazil. However, bioaccessibility tests have not yet been conducted on those materials, which is essential for better health risk estimates. This study aimed at evaluating As bioaccessibility in samples from a gold mining area located in Brazil and assessing children's exposure to As-contaminated materials. Samples were collected from different materials (a control and four As-contaminated soils/sediments) found in a gold mine area located in Paracatu (MG), Brazil. Total and bioaccessible As concentrations were determined for all samples. The control soil presented the lowest As concentrations, while all other materials contained high total As concentrations (up to 2,666 mg kg(-1)) and low bioaccessible As percentage (<4.2%), indicating a low risk from exposure of resident children next to this area. The calculated dose of exposure indicated that, except for the pond tailings, in all other areas, the exposure route considering soil ingestion contributed at most to 9.7% of the maximum As allowed ingestion per day (0.3 μg kg(-1) BW day(-1)).