Aged biochar changed copper availability and distribution among soil fractions and influenced corn seed germination in a copper-contaminated soil.

Biochar has been recommended as a multi-beneficial amendment for the in situ remediation of heavy metals contaminated soils due to its high recalcitrance, stability, specific surface area and retention capacity, which leads to a long-lasting influence on the immobilization of soil contaminants. The influence of biochar on the availability of heavy metals such as copper is not fully understood and may be related to a change in copper association with soils fractions. Therefore, a long-time laboratory incubation study was set up as a completely randomized design to test the effect of biochar from different sources (coconut husks-CHB, orange bagasse-OBB and sewage sludge-SSB) at two rates of application (30 and 60 t ha-1) on the distribution of copper in a copper-contaminated soil after 24 months incubation. Copper distribution was evaluated through a sequential extraction procedure that fractionated copper into five fractions: F1 (soluble and exchangeable), F2 (specifically bound), F3 (organic matter bound), F4 (Fe and Mn oxide bound) and F5 (residual). Copper availability, soil pH and organic matter were also evaluated. Corn seeds were germinated in the incubated biochar soil to investigate the effect of biochar on seed germination and plantlets characteristics. All biochars increased soil pH and the concentration of oxidizable organic matter, and reduced copper availability after the 24 months incubation. CHB caused a discrete influence on copper distribution among soil fractions. OBB30 increased F1 (54.5%), F3 (24.0%), F4 (32.2%) and F5 (64.1%), and reduced F2 (39.8%); OBB60 reduced F1 (61.8%), F2 (16.5%) and F3 (16.0%) and increased F4 (18.0%) and F5 (84.4%). SSB30 strongly reduced Cu concentration in F1 (96.2%), F2 (34.0%), and F3 (22.2%), and increased F4 (54.4%); SSB60 reduced F1 (57.5%) and F3 (59.4%). Considering the high stability of biochar, the association of copper to the organic fraction leads to a long-time reduction in copper availability in the contaminated soil, which can reduce the cost and increase the efficiency of the remediation process. SSB reduced seed germination but produced vigorous and well-developed plantlets. Therefore, with proper production procedure to reduce the volatile matter content, SSB may not interfere with seed germination and has the greatest potential to be used for the remediation of copper-contaminated sites.

Nitrogen and phosphorus uptake efficiency in Indian mustard cultivated during three growth cycles in a copper contaminated soil treated with biochar / Eficiência de absorção de nitrogênio e fósforo em mostarda indiana cultivada por três ciclos sucessivos em um solo contaminado com cobre e tratado com biocarvão

ABSTRACT: Biochar has been used worldwide as an efficient soil amendment due to its beneficial interaction with soil particles and nutrients; however, studies on the effect of biochar on the availability of nutrients such as N and P in tropical soils are still missing. The objective of the study was to evaluate the effect of different types and doses of biochars on the concentration and uptake of N and P in Indian mustard plants (Brassica juncea L.) grown in a Cu contaminated soil during three successive growth cycles. The greenhouse experiment was set up as randomized block design in a 3x3 factorial scheme, with 3 types of biochars (coconut shell, orange bagasse and sewage sludge) and three rates of application (0, 30 and 60t ha-1), and 4 replicates. Biochar increased plant growth by approximately 30 to 224%; however, the orange bagasse biochar was the most effective. Biochar reduced plant N concentration in approximately 15-43%, regardless of the rate of application, indicating the need to carefully adjust N fertilization. In the last growth cycle, biochar from coconut shell and orange bagasse improved the N uptake efficiency suggesting a better amelioration effect with ageing in soil. Biochar did not affect P nutrition in Indian mustard to a great extent; however, it significantly decreased the N:P ratio in the plant.

RESUMO: O biocarvão tem sido usado mundialmente como um eficiente insumo agrícola devido à sua interação benéfica com as partículas e os nutrientes do solo. Contudo, seu efeito na disponibilidade de nutrientes como N e P em solos tropicais tem sido pouco investigado. O objetivo do estudo foi avaliar o efeito de diferentes tipos e doses de biocarvão na concentração e na eficiência de absorção de N e P em plantas de mostarda indiana (Brassica juncea L.) cultivadas em solo contaminado com cobre, em três ciclos sucessivos de cultivo. O estudo foi desenvolvido em delineamento de blocos casualizados, em esquema fatorial 3x3, em casa de vegetação, com três tipos de biocarvão (casca de coco, bagaço de laranja e lodo de esgoto) e três doses (0, 30 e 60t ha-1). Todos os biocarvões aumentaram o crescimento das plantas, com variação de 30 a 224%. No entanto, o biocarvão de bagaço de laranja foi o mais eficiente. A presença de biocarvão reduziu a concentração de N nas plantas em torno de 14 a 43%, independente da dose aplicada, indicando a necessidade de monitoramento mais cuidadoso da fertilização nitrogenada. Os biocarvões de casca de coco e bagaço de laranja melhoraram a eficiência da planta na absorção de N no terceiro ciclo de cultivo, indicando melhor efeito com o tempo de contato como o solo. O uso de biocarvão teve pouca influência na nutrição fosfatada na mostarda indiana, mas diminuiu significativamente a relação N:P.