The utilization of agricultural waste as biochar for optimizing swampland: a review

The utilization of agricultural waste as biochar is one way to manage agricultural waste to encourage swamps optimization. There is quite a lot of agricultural waste in Indonesia estimated to reach 10.7 t y−1, including rice-husks, cocoa pods, coconut-shells, oil palm shells, and corncobs. One of the management of agricultural waste is to make biochar from various sources of raw materials. This paper is intended to provide information about agricultural waste as biochar in agriculture to optimize swampland in Indonesia. The quality of biochar depends on raw materials, incinerator, combustion temperature, and the length of combustion. The application of biochar on agricultural land serves as a soil enhancer that can improve its chemical properties and soil physical properties. Improvements in the quality of the soil chemical and physical properties impact the availability of nutrients and water through the ability of biochar to retain nutrients and water. In the end, the addition of biochar has implications for increasing the productivity of food crops. In the future, it is expected that with the application of biochar, swamplands can increase productivity.


Introduction
Swampland is one of Indonesia's most extensive agroecology and has considerable potential for agricultural development now and in the future, but its utilization has not been carried out optimally. Tidal swamp land consists of mineral soil (sulfuric acid) reaching 7.55 million ha and peat reaching 1.37 million ha, while lebak swamp land consists of mineral land reaching 11.64 million ha and peat reaching 13.56 million ha [1]. However, swamps are generally marginal and infertile so proper management is needed. Swamp management requires specific technologies including improving soil conditions through amelioration. Farmers in swampland often use ameliorant materials such as lime, manure, and ash [2]. Proper management of swamps will make a real contribution to Indonesia's food security. However, along with the declining quality of the soil and the environment, efforts are needed to manage swampland wisely (wise use) based on sustainability and safe for the environment.
When this has begun to develop globally, biochar/charcoal from agricultural waste as an alternative soil enhancer. Biochar is produced through a process of thermal decomposition of organic matter under conditions of limited oxygen. Similar to charcoal produced from natural combustion, but different because of its function as an amendment to the ground [3,4]. Biochar can be produced from various biomass sources such as plant residues, plant waste or animal waste. The characteristics of biochar depend on the raw material and pyrolysis conditions such as temperature, time duration and oxygen supply [4]. Biochar has demonstrated the ability to improve soil chemical properties such as pH [5,6,7,8], nutrient availability [9], nutrient and water retention [10,11,12] and cation exchange capacity [10,6,7,13], reducing N fertilizer loss [14] and reducing nutrient leaching [15,16]. Also, on  (34) In swamps, the raw materials for making biochar with high levels of abundance include rice husks, corn straw, rice straw, kalakai, karamunting, galam, bamboo, palm oil cake, palm leaves, palm fronds, oil palm bunches, coconut shells and purun tikus. The characterization and analysis of cellulose content, hemicellulose, and C / N ratio of each biochar material are presented in table 2. The highest lignin levels are found in raw materials kalakai (35.76%) and the lowest in corn straw (17.03%). High lignin content makes it difficult for organic matter to decompose [35]. The highest cellulose content was found in organic matter from oil palm cake (34.45%) and the lowest was in organic matter from corn straw (17.03%), in contrast to hemicellulose content. Hemicellulose is an amorphous polymer associated with cellulose and lignin, easy to undergo depolymerization, hydrolysis by acids, are alkaline, and easily dissolve in water. Hemicellulose has a bond with lignin stronger than a bond with cellulose and easily binds to water. Hemicellulose levels differ in the type of needle-leaf wood and broad-leaf wood [36].  [37] One way to increase the effectiveness and efficiency of biomass waste is by carbonization using pyrolysis technology. A pyrolysis is a complex event, where organic compounds in biomass are ICSTSI 2020 IOP Conf. Series: Materials Science and Engineering 980 (2020) 012065 IOP Publishing doi:10.1088/1757-899X/980/1/012065 4 decomposed by heating without oxygen. Only the volatile matter is released, while the carbon remains in it, this process occurs at temperatures above 300 ° C for 4 -7 hours [38].
The chemical and physical properties of biochar determine the quality of biochar (table 3), and these properties are determined by the type of raw material (softwood, hardwood, rice husk, etc.) and carbonization method (The type of combustion tool, temperature), and the form of biochar (solid, powder, activated carbon) [39,40]. The characteristics of biochar are influenced by the base material itself and have different effects on soil and plants [27].  [41]; 2) Nurida [42]; 3) Dariah [43]; 4) Santi dan Goenadi [44] Interest in biochar as a soil reformer has recently overgrown. In biochar production biochar, pyrolysis slow to have multiple benefits that include waste management, renewable energy production, climate change mitigation and adaptation, as well as agricultural productivity [45].

The Role of Biochar in Optimizing Swampland
Swamplands are lands throughout the year or during a long time in a year, always saturated with water or flooded [46]. Swamp is included in suboptimal land because it has low productivity due to internal and external factors [47]. Utilization of sub-optimal land, including swamps, will be the foundation of future expectations, but requires technological innovation to overcome obstacles following the land's characteristics and typology.
Tidal swamps are swamps that are affected by tides. Based on soil classification [48], tidal swamps are characterized by aquatic conditions (saturated with water) and have sulfidic material (iron sulfide) or pyrite, generally reacting with extreme acidity (pH <4) so it is often called acid sulphate soil [46]. This land generally has a low level of fertility and productivity so that agricultural development requires technological input.
The freshwater swamp is a swampland that is not influenced by tides but is inundated by river overflows for at least three months with a pool of at least 50 cm [46]. The chemical nature of the soil in the swamp swamplands is very dependent on the type of soil. Mineral soil (river sediment) has a clay texture and pH of 4.5 to 6.5. Every year the lebak land gets silt from the upper area (upstream area), so that the soil fertility is classified as moderate. Generally, N, P, and K values are low to moderate, but Ca and Mg content and CEC are generally moderate to high. The high or low nutrient content is influenced by the amount of nutrient contribution from the upstream area that enters through water run-off. This land is suitable for agricultural business. The problem only lies in the dynamics of water levels that are difficult to predict.
Peatlands consist of mostly organic matter which is weathered, with ash content equal to or less than 35%, peat depth equal to or more than 50 cm, and organic carbon content according to its weight of at least 12% [49]. Peatland development for agriculture faces biophysical land, socioeconomic and The utilization of biochar in swamps as ameliorant has not been done much. Biochar is a carbonrich solid material formed through the combustion process of organic or biomass materials without or with little oxygen (pyrolysis) at 250-500 °C. Unlike organic matter, biochar is stable for thousands of years when biochar is mixed into the soil and can absorb carbon [25,50,51].
Biochar is a pyrolysis residue in charcoal that contains high carbon and is useful for agriculture especially, for improving physical, chemical, and biological soil properties. The addition of biochar can improve soil fertility and restore degraded soil quality [52,10]. Biochar can improve the soil by increasing pH, retaining water, retaining nutrients, increasing biota activity, and reducing pollution [11]. The availability of P, soil pH, K, and Ca-dd increases with biochar application biochar [6].
Biochar can increase plant productivity directly or indirectly. The influence of biochar directly through the donation of nutrients released, while indirectly through the improvement of soil buffering capacity in holding nutrients [11, 53,12], increasing soil pH [8,5,7], and the increase in CEC, improvement of soil physical properties and their effects on microbial function and population. Biochar can reduce nutrient loss through leaching, to improve fertilizer efficiency [15,16]. The provision of biochar can reduce N fertilizer losses [14,21,22,54]. This also applies to P nutrients that are not retained by ordinary organic matter. Biochar is more able to survive in the soil than other organic materials [25]. The biochar function works, absorbs and binds water, and supplies calcium and magnesium elements to plants.
A good combination of air and water for soil microbial growth is in biochar. Useful carrier material for the microbes also exists in biochar, which can make biological fertilizer [18], biochar micropores, fungi can sporulate because low competition occurs with other saprophytes [23]. Nugraheni [57] added that biochar could increase soil fertility and provide suitable habitat for soil microbes that can even hold water and nutrients to be more available to plants. Masulili [6] applied biochar to acid sulphate soils. It reduced Al-dd, dissolved Fe, increase porosity, pH, P, CEC, Ca-dd, and K-dd. The combination treatment of biochar and chicken manure can increase the yield of Inpara-3 rice. Improvement of soil chemical properties through biochar and other ameliorant administration also impacts increasing rice yields in acid sulphate soils [6].
According to Ferizal [56] the provision of biochar as a soil enhancer derived from the combustion of agricultural waste with limited oxygen has excellent ability as a material change in soil because organic C still survives in carbon black. Biological charcoal produced from this combustion will produce activated carbon, which contains minerals such as calcium or magnesium and inorganic carbon, biochar is widely used as ameliorant material to improve soil quality, especially marginal soils [57]. So that biochar can be a substitute for growing media in plants. The biochar structure, which has a micropore can increase water's holding capacity [18,19,20].
Soil chemical properties sub-optimal land can be improved by applying biochar, including acid sulphate tidal swamps and peatlands. Biochar can increase soil pH, total N, available P, and K-dd in an acid dry land, dry climate dry land, tidal swamps, and peatlands (table 4). The increase in crop production occurs due to the application of biochar in swamps (table 5). Application of rice husk biochar increases rice yield in tidal land reaching 4.35 -5.36 t / ha [58]. On peatlands, there was an increase in corn yield due to the administration of rice husk biochar to 59% [60]. Biochar also provides increased soybean crop production in sub-optimal land. Giving rice husk biochar 10 t / ha increases the dry weight of soybean seeds to reach 2.5-2.9 t/ha [61].

Conclusion
One effort to manage agricultural waste is by making biochar. Biochar utilization opportunities for agricultural land are tremendous, both in terms of the availability of raw materials and their functions. Biochar application can be a solution in the use and optimization of swampland. Biochar in swampland plays a role in improving soil properties both, physical, chemical, and biological so that land productivity can increase. Plant productivity also increases in line with the improvement in land quality. The effectiveness of biochar in improving soil properties is influenced by biochar type, biochar manufacturing process, dosage, application method, biochar size, and soil type. The use of biochar is an alternative effort to improve soil fertility and improve the environment in a sustainable and easy and inexpensive way.