Alleviating heavy metal stress with the use of biochar application

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Pakistan’s economy is highly dependent on its agriculture sector. Due to devastated impacts of changing climate, the hydrological cycles have been disturbed which has resulted in acute shortage of surface fresh water across the globe and Pakistan is among the top targeted area. The underground water reservoirs have also been turned useless due to brackishness, moreover poor farming community of Pakistan are unable to pumping of underground water. Thus, the farmers are compelled to use raw sewage effluents as a cheapest source of irrigation, additionally it also provides high amount of nutrients. Industrial effluents discharged from these industries are irrigating chunk of agricultural soils that causes problem of metal pollution. The untreated industrial effluents are the main source of metal pollution of peri-urban soils in developing countries. Among these pollutants, inorganic heavy metals/loids like arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb) etc. are the most toxic for the agricultural sustainability and food security. These heavy metals cause negative impacts on crops production and animals health. Heavy metals pose detrimental effects on physiological and biochemical functions of plants due to their noxious nature. The transfer of these heavy metals through food chain is also a huge risk for human health.

Different organic and inorganic amendments are used to remediate the heavy metals in soil matrix. These techniques may include plant growth regulators (PGRs), application of mineral nutrients, silicon application, use of organic amendments such as compost, manure, biochar etc. Among these organic amendments biochar is well known for more efficiently immobilizing the heavy metals in the soil. Biochar is a carbon-rich solid compound obtained by heating biomass with little or no oxygen. Numerous materials can be used as feedstock, including sludge, residual plant materials and manures. Typically, biochar has high cation exchange capacity and are alkaline in nature. Biochar is potentially beneficial for improving soil properties due to large surface area, active functional group, microporous structure, high pH and higher cation exchange capacity. Due to large surface areas, it restricts heavy metals mobility by making complexes on their surface. Alkalinity of biochar can also be partially responsible for the lower concentrations of available heavy metals found in biochar-amended soils. Higher pH values after biochar addition can result in heavy metals precipitation in soils.

Biochar has potential to increase water holding capacity and plant-nutrient retention in many soils. Biochar can stabilize heavy metals in contaminated soils, improve the quality of the contaminated soil and has a significant reduction in crop uptake of heavy metals. The application of biochar is very effective for the reduction of heavy metals in soil. Hence, it can be concluded from above discussion, biochar is the best option to overcome and/ or to reduce heavy metal uptake in plants and ultimately increase the plant growth.  Biochar application in metal contaminated soils has potential to suppress the bioavailability and phyto-toxicity of metals. In addition, biochar amendment enhanced plant growth and dry biomass by improving essential trace metal availability. In such critical situation farmers should be educated to adopt new technology to enhance the crop production on sustainable basis. Therefore, as a scientist we are focusing on best method of biochar application to produce maximum yield.

 This article is collectively authored by Hinnan Khalid, Muhammad Zia-ur-Rehman and Muhammad Zeeshan


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