Unveiling Black Gold: Biochar
Since the formation of healthy soils takes centuries to millennia, but their degradation can occur very rapidly, biochar seems to be a great promise as a sustainable soil amendment. Thanks to properties such as alkaline pH, high specific surface area and porosity, elevated carbon content and metal(loid) sorption capacity it is used in the environmental remediation sphere.
Biochar applications are linked to climate change, agroecosystems and contaminated soils because biochar simultaneously immobilize contaminants, decreases greenhouse gas (GHG) emissions while helping to address the soil fertility issue, often based on the hypotheses that the input of a stable form of carbon to soil, which will remain stable for centuries to millennia, will result in prolonged improvements to some soil characteristics.
However, the use of biochar is still under study. There is increasing evidence that biochar does not always have favorable effects on soil and soil biota and that the impacts on a particular (micro)organism cannot be generalized. Additionally, despite its long-term stability, biochar undergoes chemical, physical, and biological changes over time, which makes qualitative and quantitative predictions of any effects very difficult.
Therefore, studies on the potentially detrimental effects of biochar in soil are required. Here, I will introduce some controversy about this magical material.
Using biochar as a soil amendment:
The use of biochar in soil is proposed as a method to manage soil contamination, improve mineral nutrient availability, and address soil acidity, leading to enhanced crop yields. However, the positive effects depend on specific factors such as biochar properties, plant types, agricultural practices and soil types. Some studies suggested, in an attempt to keep the soil moisture and provide water for plants more easily, the use of biochar. In some of them, biochar retained water so strongly that it reduced the availability of water to plants, as opposed to expected. In a similar way, biochar could also reduce the effectiveness of herbicides and pesticides in soil, and difficult nutrient uptake by crops due to his looking forward property of adsorb compounds.
Greenhouse gas (GHG) mitigation using biochar:
The large-scale application of biochar in soil is often touted as an efficient strategy for carbon sequestration. But the stability of biochar against oxidation varies depending on soil properties and biochar origin, making the impact on GHG emissions specific to each case. Life-cycle analyses have been used to assess the GHG mitigation effects of biochar, but results are influenced by assumptions and methods, making it challenging to compare different biochar systems or draw definitive conclusions. When evaluating biochar’s suitability for GHG mitigation over short and long timescales, it’s essential to consider potential GHG budgets for alternative uses of biomass.
Toxic contaminants in biochar itself:
Biochar application to soil can lead to increased levels of toxic compounds in the soil due to their presence in biochar. A significant challenge in the use of biochar is that toxic substances can be released from the biochar matrix, for example, due to biochar aging, and affect living organisms. The presence of contaminants in the biochar could happen because of the use of contaminated feedstock for biochar production. Some of the implications involved in this aspect are: Decreased plant growth, inhibition, mortality, genotoxic effects, human health risk in case of metal(loids) distribution in the environment and their accumulation in the crop biomass/food chain.
Conclusion:
Biochar is not a panacea, and it needs to be part of an integrated management system. Not all biochar are suitable for all soils and all purposes. Moreover, due to the lack of long-term studies we are not able to predict the evolution of the biochar in the soil and its implications, for example because of the aging process and potential secondary contaminations. As with any innovative technology, the application of biochar in soil remediation is not without its skeptics and controversies. This is not black or white, it all needs a holistic point of view of management.
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