|Himawan Tri Bayu Murti Petrus||Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika 2, Yogyakarta 55281, Indonesia|
|Andreas Diga Pratama Putera||Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika 2, Yogyakarta 55281, Indonesia|
|Inasanti Pandan Wangi||Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika 2, Yogyakarta 55281, Indonesia|
|Muhammad Aulia Ramadhian|
biochar was added to modify ureic fertilizer in order to control nitrogen
release in two methods: (1) mixed-granule and (2) as a coating. The mixed-granule
fertilizer was made of varied compositions of rice husk biochar, ureic fertilizer,
and clay as a binder, whereas the coating model was formulated from ureic
fertilizer, biogas sludge, and clay as a core and coated with various
compositions of biochar and clay. All of the samples were leached by 100 mL of
water once every three days, and the leachate was analyzed for its nitrogen
content. Of all
samples, coated fertilizer with a composition of 20% biochar and 80% clay showed
the slowest nutrient diffusion with an effective diffusivity (De) number of
2.85×10-8 cm/s2. The results show that both models
increase fertilizer’s ability to hold nitrogen longer than pure fertilizer.
Both methods, mixed-granule and coated, showed slow release rate patterns,
particularly at the beginning of the leaching process, and held the nitrogen
content longer. Both models’ release rates enable the modification of nitrogen
release to meet the need for nitrogen in certain plantations.
Rice husk biochar was added to modify ureic fertilizer in order to control nitrogen release in two methods: (1) mixed-granule and (2) as a coating. The mixed-granule fertilizer was made of varied compositions of rice husk biochar, ureic fertilizer, and clay as a binder, whereas the coating model was formulated from ureic fertilizer, biogas sludge, and clay as a core and coated with various compositions of biochar and clay. All of the samples were leached by 100 mL of water once every three days, and the leachate was analyzed for its nitrogen content. Of all samples, coated fertilizer with a composition of 20% biochar and 80% clay showed the slowest nutrient diffusion with an effective diffusivity (De) number of 2.85×10-8 cm/s2. The results show that both models increase fertilizer’s ability to hold nitrogen longer than pure fertilizer. Both methods, mixed-granule and coated, showed slow release rate patterns, particularly at the beginning of the leaching process, and held the nitrogen content longer. Both models’ release rates enable the modification of nitrogen release to meet the need for nitrogen in certain plantations.
Coated fertilizer; Granule fertilizer; Nitrogen release; Rice husk biochar
As an agrarian country with rice as its main staple, Indonesia is one of the main rice producers. Rice production has been increasing each year. This paddy grain is constituted by 20–30% husk, with rice husk waste amounting to the range of 11,000,000–14,000,000 tons every year (Pode, 2016). However, rice husk can also be a valuable material if it is well processed. One example is to convert rice husks into biomass charcoal in the form of a briquette used for solid fuel combustion and gasified to produce syn-gas (Dafiqurrohman et al., 2016). The other example is for soil remediation, usually applied for clay or limestone (Shen et al., 2014) and the extraction of amorphous silica (Dhaneswara et al., 2020). In this work, we study the use of biochar from rice husk as a slow-release fertilizer agent.
One of the most popular methods to produce biomass is the slow pyrolisis method that turns biomass into charcoal. Charcoal’s characteristically porous body provides an ideal habitat for soil microbes, but it is not consumed like other organic compounds. It can also hold the water and nutrients needed for crops (Shen et al., 2014). Biochar as a soil enhancer
provides better humidity and fertility to the soil. This application also supports the carbon-negative concept that minimizes the amount of carbon accumulation in the open air by adding it into the soil. Biochar also acts as a repair agent in the soil that changes its physical, chemical, and biological characteristics (Manyà et al., 2018; Zhu et al., 2019).
The usage of agricultural fertilizer in Indonesia is currently dominated by urea. Due to its ease of use, a high level of crop production and government subsidies further increase farmers’ consumption of this nitrogen-based fertilizer (Winanto, 2018). Although currently, the government has started to promote the use of organic fertilizer due to its production limitation and higher price, urea remains the most-used fertilizer, providing about 60% of the total fertilizer needs in Indonesia each year.
Urea is specially created to supply nitrogen to crops, but unfortunately, there is a lack of efficiency in nitrogen supplying crops. From the amount of fertilizer shown, about 20–65% of the urea is wasted. The nitrogen loss in the fertilizer used occurs because of evaporation as NH3, immobilization in soil pores or being carried away along with water. These inefficiencies cause adverse effects to the environment as excess nitrogen changes soil pH, which kills microbes in the soil, and leached fertilizer can poison water that may be consumed by human and animals. To fulfil the nitrogen supply to crops and increase harvests, many farmers have increased their use of urea, which results in worse pollution and excessive use of fertilizer (Bari et al., 2007; Nardi et al., 2018).
To decrease the adverse effect of urea and reduce the consumption of urea, there is a need to increase usage efficiency. Several experiments have shown that one of the most efficient methods is controlling the release of various fertilizer constituents, like nitrogen, into the soil. An experiment by Zhang et al. (2018) revealed that, using controlled-release urea, the urea needed was decreased by 50%, but the crop yield increased by 20–28%. Another experiment examining the effect of controlled-release urea by Nardi et al. (2018) showed that the use of slow-release urea promoted higher microbial activity and lower-pH soil, which reduces the harmful effect of urea on the soil. The method of producing slow-release fertilizer has itself been researched extensively, with Lateef et al. (2016) using nano-zeolite to encapsulate fertilizer, resulting in soil’s increased water retention and promoting fertilizers’ absorption efficiency into the soil. An experiment by Zhang et al. (2014) used graphene oxide (GO) as the coating for a potassium-based fertilizer. The release of potassium ions took place after seven to eight hours, with about 93.8% of potassium ions released from the fertilizer. An experiment using GO was also conducted by Andelkovic et al. (2018) for P-based fertilizer, which resulted in fertilizer absorption into the soil increasing to 99%. Moreover, GO can be produced from graphite waste, providing a circular economy and increasing the feasibility of using GO a slow-release fertilizer or in any other utilization (Kusrini et al., 2019; Kusrini et al., 2020). Muharam et al. (2015) studied the release of potassium chloride from chitosan microspheres as a slow-release fertilizer.
In the current study, rice husk waste from agricultural production was made into biochar and utilized as an economically and environmentally friendly alternative coating agent for urea. The fertilizer in this experiment was modified with the addition of a mixture of rice husk biochar and clay. Biochar itself has been found to have a beneficial effect on soil and crop yields as its porous structure made up of carbon can, when added to the soil, increase the soil’s ability to store nutrients and increase water retention, decreasing heavy metal content and regulating soil pH (Zornoza et al., 2016; Chen et al., 2018). Nitrogen release is also assessed using a mathematical model. The models are divided into two forms, granule mixture and coated fertilizer, as Figure 1 shows.
The experiment with granule fertilizer showed that the addition of rice husk biochar can slow the release of nitrogen from the fertilizer. The results showed that the addition of more biochar into the granule slowed the release of nitrogen. The optimum amount, however, is 40% biochar, 40% urea, and 20% clay, as shown. The addition of more biochar did not affect the release rate, other than the initial release. The experiment with coated fertilizer showed that decreasing biochar content in the coating slowed the nitrogen release. The slowest release of nitrogen was obtained with 80% clay and 20% biochar content. This phenomenon is due to biochar’s hydrophobicity, which makes the coating more brittle at high biochar content, such that it will leak nitrogen. High clay content also acts as a binder to prevent the release of nitrogen into the soil. The De value obtained from the 80% clay and 20% biochar sample was 2.85×10-8 cm/s2. Because of the differences in nitrogen absorption for every type of plant, the coating method chosen can be suitable for the absorption system. This result shows that biochar is a prospective slow-release agent in minimizing the inefficiency of fertilizer usage. The use of biochar provides a circular economy for farmers dealing with rice husk waste from paddies’ production.
We gratefully acknowledge the Department of Chemical Engineering, Energy Conservation and Environmental Protection Laboratory for the provided facilities to complete this study.
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