Converting abundant agricultural residues to valuable products, such as biochar, is a pressing challenge for society. Here, our objective has been to produce biochar-based fertilizers (BBFs) with high carbon stability, high yield, and characteristics favorable for their use in soils. Thus, H 3 PO 4 with and without MgO was co-pyrolyzed with coffee husk and poultry litter. Proximate analysis, total phosphorus and magnesium, biochar yield, carbon retention, and thermal and chemical carbon stability were assessed. The BBFs were slightly acidic (pH ∼6.0) and showed high contents of total P (146−206 g kg −1 ) and total Mg (96−98 g kg −1 ), similar to commercial fertilizers. Biochar yield increased up to 65% when treated with H 3 PO 4 and H 3 PO 4 −MgO, resulting in up to 78% greater carbon retention. BBFs showed higher thermal stability, by thermogravimetric analysis and muffle oxidation, when compared to corresponding pristine biochars. Conversely, the addition of H 3 PO 4 −MgO decreased the chemical stability (higher H 2 O 2 and K 2 Cr 2 O 7 oxidation), compared to the biochars, because of the increase in surface area and reactivity. We concluded that the co-pyrolysis of biomasses with H 3 PO 4 and MgO promoted thermal stabilization (increased yield) and increased chemical oxidation, because of increased surface area and reduced crystallinity of the BBFs.
The forage grasses are explored for the phytoremediation of heavy metals from contaminated areas. The present study evaluates the tolerance of forages grasses to Pb and the availability of Pb for the Mehlich 1, DTPA, and USEPA 3051 and 3052 extraction methods. The forage grasses cultivars Panicum maximum cultivars Aruana and Tanzânia, Brachiaria decumbens cultivar Basilisk, Brachiaria brizantha cultivar Xaraés and Marandu were assessed. Each cultivar was grown in a greenhouse in Diamantina, Brazil, in Typic Hapludox (Oxisol). The Pb was applied to the soil at doses of 0, 45, 90 and 270 mg kg-1 soil in a randomized design with four replications. The experiment was conducted over a 90-day trial period. Increasing Pb doses in the soil caused a reduction of growth in all varieties studied, and the "Basilisk" forage was generally more tolerant to Pb, while the Xaraés forage was generally more susceptible to the addition of Pb. The lower transfer coefficient of the cultivar "Basilisk", due to the high Pb content and accumulation in its roots, makes it the most suitable for phytoremediation programs, with possible uses in pasture areas. None of the varieties can be considered a Pb hyperaccumulator. The Mehlich 1, DTPA, USEPA 3051 and USEPA 3052 extraction methods indicated different doses of Pb in the soil, and the Mehlich 1 method demonstrated the lowest level of metal extraction from the soil. No correlation was observed between the forage grasses growth and the measurement of Pb in soil by the studied extraction methods, especially for the Mehlich 1 and DTPA methods, suggesting the inefficiency of these techniques for determining the phytoavailability of Pb.
A mineração tem promovido um grande aumento na ocorrência de áreas degradadas advindas de atividades mineradoras no Brasil. O objetivo deste trabalho foi avaliar o crescimento da candeia sob a influência da adubação mineral e orgânica quando cultivada em rejeito da mineração de quartzito. Conduziu-se um experimento em casa de vegetação em delineamento experimental inteiramente casualizado com quatro repetições. Os tratamentos consistiram de cinco combinações de adubação orgânica (AO) e mineral (AM) e um tratamento adicional do rejeito sem AO e AM (Controle). As combinações foram: 0%AO/100%AM; 25%AO/75%AM; 50%AO/50%AM; 75%AO/25%AM; 100%AO/0%AM. As doses de 100% de AM e AO foram de 0,15 gde N, 0,32 gde P2O5, 0,18 g de K2O e 5 g de esterco de curral por dm³ de rejeito. A candeia respondeu positivamente à adubação mineral e orgânica com as doses recomendadas de 0,075 g N, 0,16 g P2O5 e 0,09 g K2O e 2,5 g de esterco de curral, por dm3 de rejeito da mineração de quartzito. O acúmulo de nutrientes na espécie candeia foi na seguinte ordem na parte aérea: K > N > P > Ca > Mg >S > Mn > Fe > B > Zn > Cu.Palavras-chave: Área degradada; teor adequado; estado nutricional; espécie nativa. AbstractGrowth of Eremanthus erythropappus by mineral and organic fertilization on mining reject of quartzite. There is a large increase of degraded areas as result of mining activities in Brazil. This research aims to evaluate growth of the Eremanthus erythropappus on mining reject of quartzite, under the influence of mineral and organic fertilizer. We developed an experiment in a greenhouse, in completely randomized design with four replications. The treatments consisted of five combinations of mineral (MF) and organic (OF) fertilizer, and an additional treatment of mining reject without MF and OF (witness). The combinations were as follows: 0%OF/100%MF; 25%OF/75%MF; 50%OF/50%MF; 75%OF/25%MF; 100%OF/0% MF. Doses of 100% MF and OF were: 0,15 g of N, 0,32 g of P2O5, 0,18 g of K2O, and 5 g of bovine manure per dm³ of mining rejects. The Eremanthus erythropappus responded to mineral fertilization with recommended doses of 0,075 g N, 0,16 g P2O5 and 0,09 g K2O and 2,5 g of bovine manure per dm³ of mining reject of quartzite. The accumulation of nutrients in the species Eremanthus erythropappus on the shoot was as follows: K > N > P > Ca > Mg >S > Mn > Fe > B > Zn > Cu.Keywords: Degraded area; nutritional status; nutrients accumulation; native species.
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