Why are so many celebs suddenly caring about smog? - Page 3

What is biochar?

Biochar is a solid material obtained from the carbonization thermochemical conversion of biomass in an oxygen-limited environments. In more technical terms, biochar is produced by thermal decomposition of organic material (biomass such as wood, manure or leaves) under limited supply of oxygen (O₂), and at relatively low temperatures (<700C). This process mirrors the production of charcoal, which is perhaps the most ancient industrial technology developed by humankind. Biochar can be distinguished from charcoalused mainly as a fuelin that a primary application is use as a soil amendment with the intention to improve soil functions and to reduce emissions from biomass that would otherwise naturally degrade to greenhouse gases.

What can biochar do?

Sustainable biochar is a powerfully simple tool that can 1) fight global warming; 2) produce a soil enhancer that holds carbon and makes soil more fertile; 3) reduce agricultural waste; and 4) produce clean, renewable energy. In some biochar systems all four objectives can be met, while in others a combination of two or more objectives will be obtained.

How is biochar produced?

Carbonization is the process of converting a feedstock into biochar through reductive thermal processing. The process involves a combination of time, heat and pressure exposure factors that can vary between processors, equipment, and feedstocks. There are two main processes: pyrolysis or gasification. Energy products in the form of gas or oil are produced along with the biochar. These energy products may be recoverable for another use, or may simply be burned and released as heat. In addition, biochar can be made from a wide variety of biomass feedstocks. As a result, different biochar systems emerge on different scales. These systems may use production technologies that do or do not produce recoverable energy as well as biochar, and range from small household units to large bioenergy power plants.

How do we know that biochar helps increase crop yields?

There is a large body of peer-reviewed literature quantifying and describing the crop yield benefits of biochar-amended soil. Field trials using biochar have been conducted in the tropics over the past several years. Most show positive results on yields when biochar was applied to field soils and nutrients were managed appropriately.

There is also evidence from thousands of years of traditional use of charcoal in soils. The most well-known example is the fertile Terra Preta soils in Brazil, but Japan also has a long tradition of using charcoal in soil, a tradition that is being revived and has been exported over the past 20 years to countries such as Costa Rica. The Brazilian and Japanese traditions together provide long-term evidence of positive biochar impact on soils. To read more about field trials and biochar, please see the IBI publications page.

While the larger questions concerning overall biochar benefits to soils and climate have been answered in the affirmative, significant questions remain, including the need for a better understanding of some of the details of biochar production and characterization. Work is ongoing to develop methods for matching different types of biochar to soils for the best results.

How can biochar help farmers?

Biochar provides a unique opportunity to improve soil fertility for the long term using locally available materials. Used alone, or in combinations, compost, manure and/or agrochemicals are added at certain rates every year to soils, in order to realize benefits. Application rates of these can be reduced when nutrients are combined with biochar. Biochar remains in the soil, and single applications can provide benefits over many years. Farmers can also receive an energy yield when converting organic residues into biochar by capturing energy given off in the biochar production process. In both industrialized and developing countries, soil loss and degradation is occurring at unprecedented rates, with profound consequences for soil ecosystem properties. In many regions, loss in soil productivity occurs despite intensive use of agrochemicals, concurrent with adverse environmental impacts on soil and water resources. Biochar can play a major role in expanding options for sustainable soil management by improving upon existing best management practices, not only to improve soil productivity but also to decrease nutrient loss through leaching by percolating water.

How does biochar affect soil biology?

Decades of research in Japan and recent studies in the U.S. have shown that biochar stimulates the activity of a variety of agriculturally important soil microorganisms, and can greatly affect the microbiological properties of soils. The pores in biochar provide a suitable habitat for many microorganisms by protecting them from predation and drying while providing many of their diverse carbon (C), energy and mineral nutrient needs. With the interest in using biochar for promoting soil fertility, many scientific studies are being conducted to better understand how this affects the physical and chemical properties of soil and its suitability as a microbial habitat. Since soil organisms provide a myriad of ecosystem services, understanding how adding biochar to soil may affect soil ecology is critical for assuring that soil quality and the integrity of the soil subsystem are maintained.

How does biochar affect soil properties like pH and CEC?

Biochar reduces soil acidity which decreases liming needs, but in most cases does not actually add nutrients in any appreciable amount. Biochar made from manure and bones is the exception; it retains a significant amount of nutrients from its source. Because biochar attracts and holds soil nutrients, it potentially reduces fertilizer requirements. As a result, fertilization costs are minimized and fertilizer (organic or chemical) is retained in the soil for longer. In most agricultural situations worldwide, soil pH (a measure of acidity) is low (a pH below 7 means more acidic soil) and needs to be increased. Biochar retains nutrients in soil directly through the negative charge that develops on its surfaces, and this negative charge can buffer acidity in the soil, as does organic matter in general.

CEC stands for Cation Exchange Capacity, and is one of many factors involved in soil fertility. "Cations are positively charged ions, in this case we refer specifically to plant nutrients such as calcium (Ca2+), potassium (K+), magnesium (Mg2+) and others. These simple forms are those in which plants take the nutrients up through their roots. Organic matter and some clays in soil hold on to these positively charged nutrients because they have negatively charged sites on their surfaces, and opposite charges attract. The soil can then "exchange these nutrients with plant roots. If a soil has a low cation exchange capacity, it is not able to retain such nutrients well, and the nutrients are often washed out with water.

Can you add biochar to alkaline soils?

Most biochar trials have been done on acidic soils, where biochars with a high pH (e.g. 6 10) were used. One study that compared the effect of adding biochar to an acidic and an alkaline soil found greater benefits on crop growth in the acidic soil, while benefits on the alkaline soil were minor. In another study, adding biochar to soil caused increases in pH which had a detrimental effect on yields, because of micronutrient deficiencies which occur at high pH (>6). Care must be taken when adding any material with a liming capacity to alkaline soils; however, it is possible to produce biochar that has little or no liming capacity that is suitable for alkaline soils.

How long does biochar persist in the soil?

Biochar is a spectrum of materials, and its characteristics vary depending upon what it is made from and how it is made. One unifying characteristic of biochars, however, is that it mineralizes in soils much more slowly than its uncharred precursor material (feedstock). Most biochars do have a small labile (easily decomposed) fraction of carbon but there is typically a much larger recalcitrant (stable) fraction. Scientists have shown that the mean residence time (the estimated amount of time that biochar carbon will persist in soils) of this recalcitrant fraction ranges from decades to millennia.

Why is biochar persistence in soils important?

The persistence of biochar when incorporated into soils is of fundamental importance in determining the environmental benefits of biochar for two reasons: first, it determines how long carbon in biochar will remain sequestered in soil and contribute to the mitigation of climate change; and second, it determines how long biochar can provide benefits to soil and water quality.

Why does biochar persist in soils longer than the original biomass from which it was made?

The carbon lattice structure made up of fused polyaromatic carbon rings is hypothesized to be the key property that confers a resistance to mineralization (conversion from organic carbon to carbon dioxide via respiration) by soil microbes that utilize organic matter i.e., hydrocarbons, as food (Lehmann et al, 2015). The energy required by microbes to access the carbon in biochar appears to be greater than that acquired when it is released. In contrast, carbon compounds in the original biomass (feedstock) are a net positive energy sources and are more readily mineralized by soil microbes.