Biochar: A vital soil amendment for degraded land



LAND DEGRADATION is an emerging issue in several countries especially in Pakistan as a consequence of climatic variabilities. Land degradation is impoverishment of the land by human activities and by natural causes. The loss of arable land has been caused by a number of factors, many or most of which are tied to human development in last 2 decades. It has been grouped into five classes: water erosion, wind erosion, soil fertility decline, salinization and water logging. Water and wind erosion takes place due to abuse of natural resources, caused by vegetation clearance and intensive tillage. Erosion also takes away fertile layer of soil. Excessive rainfalls, back to back floods and poor water management results water logging.


The primary causes of degradation are deforestation, overexploitation for fuel wood, overgrazing, agricultural activities and industrialization. Faster rate due to increasing demands of timber, fuel and forest products which results into degradation of land resources Overgrazing results into reduced growth of vegetation, reduced diversity of plant species, excessive growth of unwanted plant species, soil erosion, and degradation of land due to cattle movement.


Modern agricultural practices, excessive use of fertilizers and pesticides has adversely ruined the natural quality and fertility of the cultivation land. Development of industries for the economic growth of the country leads to excessive deforestation and utilization of land in such as way that it has lost its natural up gradation quality. On the global basis, the soil degradation is caused primarily by overgrazing (35%), agricultural activities (28%), deforestation (30%), over exploitation of land to produce fuel wood (7%), and industrialization (4%).


Biochar is a solid material obtained from the carbonization of biomass. It may be added to soils with the intention to improve soil functions and to reduce emissions from biomass that would otherwise naturally degrade to greenhouse gases. Biochar also has appreciable carbon sequestration value. These properties are measurable and verifiable in a characterization scheme, or in a carbon emission offset protocol Biochar is also known as black carbon, a product derived from organic material and is found in soils in very stable form. It can persist in soil for long periods of time at various depths, typically thousands of years. Biochar originated from the Amazon Basin which has unusually fertile soils known as Terra Pretta and Terra Mullata, these soils are rich in carbon.


Biochar has been heralded as an amendment to improve soil carbon sequestration, enhance agronomic productivity and revitalize the degraded soils. Biochar is similar to charcoal the difference of biochar with charcoal is that biochar is produced under controlled conditions with non-energy and varied uses as soil conditioner. In recent years, considerable researches have focused on biochar, its nature and its physical and chemical properties to explore its potential benefits and negative aspects, particularly for applying as an agricultural amendment as it has application to soil, animal feed mixers, water filtration, water and nutrient holding, toxic metals binder as well as soil neutralizing conditioner.


Biochar is manufactured by thermal decomposition of organic material under limited or complete absence of oxygen. There are various technological interventions available to produce it. Consideration of two things keep vital importance in production of biochar, type of feed stock and conditions under which this feed stock is heated also known as pyrolysis conditions. Biomass is super-heated in the absence of oxygen at high temperature (300°C to 1500°C) in specially designed furnaces.


There are various type of feed stocks used in the production of biochar ranging from animal manure, wood, plant residues, wood chips, wood pellets to debris or slash from forest thinning. Traditionally, kilns made from clay, bricks or steel were used to produce charcoal. However, these kilns brought about a negative environmental standing because they were related to deforestation and air pollution.


In modern method, volatile gases and hydrocarbons are captured including green house gases and can be used for bioenergy production. These captured emissions used like natural gas are known as syngas are produced along with bio-oil i.e. liquid leftovers in biochar production also used as energy source. The thermal decomposition of the organic materials results in remnant solid material produced, known as biochar. Lower temperatures (300°C-600°C) yield more solid char material and temperatures above 700ºC result in more liquid/gas components. Quality of biochar depends upon type of feed stock and pyrolysis conditions.


Many researchers have revealed that biochar has a number of benefits for soil and environment. Firstly it enhances soil fertility working as an organic amendment it improves soil physical and chemical properties. Biochar is significantly effective in increasing the soil carbon as well as organic matter content of soil. It enhances cation exchange capacity and exchangeable potassium in soil while neutralizing the pH of soil. Soil pH is affected by the pH of biochar used as amendment and pH of biochar depends upon type of feed stock and pyrolysis conditions.


Scientifically it is proved that biochar helps in lowering the bulk density of clayey soils and improves aeration and drainage of soils. Biochar is a low density porous material, it facilitates for better root penetration. Water and nutrient holding capacity of soil is improved with application of biochar. It regulates the acidifying effects of nitrogen fertilizers. Biochar is a good absorbent and it decreases leaching of nutrients. It has an advantage over compost that biochar does not decompose rapidly and it can persist in soil for hundreds of years.


Biochar enhances soil microbial life, which leads to more carbon storage in soil and nitrogen fixation. Recent studies concluded that biochar can lead to positive results on crop production. It is commonly observed that plant growth significantly enhanced when fertilizers are applied in combination with biochar.


Mitigating climate changes negative impact is an important property of biochar which is a carbon negative technology as it sequesters carbon in soil reducing the net emissions. It should be adopted for environmental management. Biochar may also adsorb pesticides, nutrients and minerals in soil, preventing the movement of these chemicals to surface water or groundwater, and the subsequent degradation of these waters from agricultural activity.


Biochar has also been demonstrated to reduce methane and nitrous oxide emissions from agricultural soils which could have additional climate mitigation effects, as these are potent greenhouse gases. According to scientists from 1850 to 2000, 34% of carbon dioxide emissions have been attributed due to land clearing. But biochar helps to capture this carbon dioxide from environment and brings back to soil.


Biochar is a simple and sustainable tool for the management of agricultural wastes. It helps in waste recycling as animal and crop wastes are used in biochar manufacturing and these wastes converted into bio-energy that is quiet useful. Not only power and energy obtained in combustion process but overall volume of waste also reduce.


Conversion of organic waste into biochar decreases methane gas which is usually generated by natural decomposition of waste material. With the use of this technique, we can store 2.2 gigatones of carbon per year. Climate change mitigation is indirectly influenced through proper waste management. This is comparatively economical, extensively applicable and readily scalable. Biochar addition to soil alters microbial populations in the rhizosphere, albeit via mechanisms not yet understood, and may cause a shift towards beneficial microorganism populations that promote plant growth and resistance to biotic and abiotic stresses. In addition there is scant evidence for biochar-induced plant protection against soil-borne diseases; the induction of systemic resistance towards several foliar pathogens has been demonstrated.


In nutshell, using biochar as a soil amendment can help sequester stable carbon in soils and combat harmful effects of climate change. However, responses to biochar may depend on the type of feed stock used and the specific characteristics of that biochar. Because biochar characteristics determine its suitability for specific agronomic or environmental purposes, biochar production must be tailored to address such specific needs and Pakistan biochar initiative has been setup in this regard.

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