Basically, porous materials will have large surface areas. The more pores, the greater the surface area of the material. Efforts to increase pores or expand the surface can be done in many ways depending on the goal. The type of pores also affects the total surface area and also the use or application of the material. For example, materials that have more micropores will have a larger surface area and have different specific uses than materials that are dominant with medium pores (mesopores) or large pores (macropores). Designing a material so that it is micropore, mesopore or macropore dominant can be done, namely by selecting raw materials and process technology, for example biochar produced from pyrolysis will produce a larger surface area compared to the initial unprocessed biomass.
In land related to use for agriculture or plant cultivation, the aspect of soil porosity or pores is an important aspect. This is mainly related to nutrient and water retention as well as soil aeration. Expanding soil pores will be very useful for improving soil quality so as to support the success of agriculture or plant cultivation. Soil that has more pore space will be able to store large amounts of water and nutrients too. Soil that has a high number of small (micropore) and medium (mesopore) pores will tend to hold water and nutrients more strongly than soil that has many large pores (macropore). And if there is evaporation or use of water by plants or a leaching process occurs in nutrients, then the large pores (macropores) left behind by the water and nutrients will follow the medium (mesopore) and micropore.
Providing organic material in the form of compost to the soil is generally used to form more micropore spaces. The more micropore spaces that are formed, the more moisture the soil will have. Soil organic matter has more pores than soil mineral particles, which means that the surface area for absorption is also greater. Providing organic material in the form of compost, apart from increasing the number of pores or soil porosity, also reduces the volume weight. This organic material or compost is a source of energy for soil microbial activity, reduces soil volume, improves soil structure, aeration and air binding capacity. Soil with high total pores, such as clay, tends to have a low volume weight, while soil with low total pores, such as sandy soil (coarse texture), tends to have a high volume weight.
Apart from increasing total pores, adding compost also increases soil pH, namely in sandy soil and acidic soil, including entisol, ultisol and andisol and is able to reduce soil exchangeable Al. The increase in pH is due to the process of breaking down the compost. The results of this overhaul will produce basic cations which can increase the pH or release basic cations from the compost into the soil so that the soil is saturated with basic cations. The weathering or decomposition process of the compost will release alkaline cations which cause the soil pH to increase.
Soil organic C will also increase with the addition of compost and total N (nitrogen). The more organic matter added to the soil, the greater the increase in organic C in the soil. Compost from animal waste has the lowest C/N ratio compared to compost from plants. Organic materials that have a high lignin content will inhibit the speed of N mineralization and the C/N ratio will be high. In fact, further decomposition of organic matter is characterized by a low C/N ratio. Meanwhile, a high C/N ratio indicates that decomposition has not yet continued or has just started. In this process there is a decrease in carbon / C and an increase in nitrogen / N.
The need for compost on marginal land such as sandy land is also much greater, reaching almost twice as much as on ordinary or standard land. Meanwhile, the need for chemical fertilizer on marginal land is usually less than on normal/standard land. Ideally, using compost at optimal doses will be able to increase plant productivity and preserve the environment.
Unlike compost which will completely decompose, as a soil amendment, biochar can last hundreds of years in the soil. Biochar, which has a large surface area, also has many micropores which increase soil porosity, like compost. Pyrolysis conditions are important in determining the quality of biochar besides the biochar raw material itself. In rough textured soils such as sandy land, biochar will improve water and nutrient retention because its micro pores slow down its release (slow velocity). The quality of biochar is directly proportional to the efficacy of biochar treatment. A number of parameters related to the application of biochar for soil improvement/treatment are also similar to compost, including: soil carbon content and mineralization, soil micro-structural & aggregation, bioavailable nitrogen, and microbial activity & diversity. Almost all biochar is not fertilizer like compost, read more details here, so inoculation (charging) of biochar before application can be done by filling the biochar pores with water containing specific chemical elements or microbes. This will produce rapid positive effects compared to biochar alone. Apart from that, biochar is also used to reduce carbon dioxide (CO2) in the atmosphere as carbon sequestration. This is very much in line with the current problems of climate change and global warming.
Biochar is a heterogeneous substance rich in aromatic carbon and minerals. Biochar is produced from the pyrolysis process (a process where organic material is decomposed at temperatures between 350 to 1000 C with well-controlled conditions of minimal or no oxygen and is widely used for soil amendment). The carbon content for biochar must be above 50%, whereas if pyrolysis products of organic material with a carbon content of less than 50% are not included in the biochar category but are referred to as pyrogenic carbonaceous material (PCM). The organic carbon content of pyrolyzed char fluctuates between the range of 5% and 95%, depending on the raw material and temperature. process used. For example, the carbon content from pyrolysis of chicken manure is around 25%, while from wood it is around 85% and bone is less than 10%. When using mineral-rich raw materials such as sewage sludge or animal waste, the pyrolysis products will contain high ash so that the total pores are smaller.
Apart from that, biochar must also have a molar ratio of H/Corg of less than 0.7 and a molar ratio of O/Corg must be less than 0.4. The molar ratio of H/Corg is an indicator of its degree of carbonization (pyrolysis) and is therefore closely related to the stability of biochar, which is one of the most important characteristics of biochar. This ratio fluctuates depending on the type of biomass used and the conditions of the production process. A ratio value that exceeds 0.7 indicates non-pyrolytic char or inadequate pyrolysis process conditions. Meanwhile, the O/Corg ratio is also used to differentiate it from other carbon products. Specific surface area is also a measure of the quality and characteristics of biochar, and also a control value for the pyrolysis method used. Although a surface area of less than 150 m2/gram can be used in certain cases, it is preferred or preferred if it is more than 150 m2/gram.
With the characteristics above, compost and biochar as well as chemical fertilizers can be used together, even in the composting process biochar can also be added to reduce N organic released into the atmosphere. Apart from increasing the number of micro pores in the soil or increasing the total pores, the nutrients from compost and chemical fertilizers will also be released more slowly (slow release). How slow release the fertilizer can be designed depends on needs, for more details you can read here. When biochar is used properly, it can maximize harvest productivity, improve soil fertility and minimize environmental impacts. Four things need to be considered when applying biochar, namely the right source of biochar, the right location (right place), the right dose (right rate) and the right time. Not all types of soil and plants will produce increased yields from biochar applications, so it is important to know what type of soil produces increased productivity. A soil map can help to identify soil types that have the potential to provide benefits or advantages from the application of biochar. Farmers can consult with agricultural consultants or professionals in the field to help with the selection and application of biochar.
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