Applications of rice husk biochar (RHB) into soil

     The application of biochar has been shown to improve soil chemical properties, and especially rice husk biochar as stated by Sovu et al. (2012) that has an advantage over inorganic fertilizers in the subsequent growth of planted seedlings and soil fertility. Biochar is made from a pyrolysis process that occurs spontaneously at extreme high temperatures that can go above 300°C. At its most extreme state, pyrolysis leaves only a carbon residue, which is called carbonization. The high temperatures used in pyrolysis induce polymerization of the molecules within the feedstocks, producing larger molecules and thermal decomposition of some feedstock components into smaller molecules. The remaining solid component following pyrolysis is charcoal, referred to as biochar, when produced with the intention of adding it to soil to improve it (Schmidt et al., 1999; Preston and Schmidt., 2006; Hussain et al., 2008). Basically, biochar is known as a pyrolized carbon from solid waste used in agriculture application since 1998.  

      In fact, using rice straw and rice husk in rice growing has been practiced for some time (Ponamperuma, 1982; Eagle et al., 2001; Singh et al., 2008; Kaewpradit et al., 2009). Williams et al. (1972) discussed the advantages and drawbacks of burning versus incorporating rice straw in rice growing. Karmakar et al. (2009) and Mahvi et al. (2005) reported the mixed effects of fly ash and rice husk ash on improving soil properties to decrease soil bulk density and to increase soil pH, organic carbon, available nutrients, and crop yield. The increase in crop yield with biochar application has also been reported for crops such as cowpeas (Yamato et al., 2006), soybeans (Tagoe et al., 2008), and maize (Yamato et al., 2006; Rodríguez et al., 2009).

Christoph Steiner (Autor)

      According to Haefele et al. (2009), the total crop residues produced each year in rice-based systems of Asia are roughly estimated at 560 million tons of rice straw and 112 million tons of rice husks (based on 2005 production, a harvest index of 0.5, and a husk/paddy ratio of 0.2). In such consideration, rice residues could be used to produce biochar to improve, maintain, and recycle nutrients in order to enhance soil fertility. Despite their high nutrients properties, biochars stability depends on the temperature used in the pyrolysis process; this stability could help to reduce greenhouse gas emission to some extent. These residues constitute a valuable resource, but actual residue management practices do not use their potential adequately and often cause negative environmental consequences. Increasing opportunity costs of organic fertilizer use and shortened fallow periods because of cropping intensification have caused a continuous decline in recycling crop residues in the past decade (Pandey, 1999).

Source: http://www.ngi.no/en/Project-pages/Biochar/Background/

     Residue burning is widely practiced and causes air pollution, human health problems, and considerable nutrient loss. 

     A publication made in the Farmers of Forty Centuries or Permanent Agriculture in China, Korea, and Japan published in 1911, details the comments of a USDA soil scientist F.H. King. He wrote of how he witnessed farmers in some sides of Asia, regularly composting and recycling all types of organic waste materials as well as ashes to use as soil amendments on their fields. This was a method farmers used to maintain soil fertility and improve crop production through centuries. Actually, this was an original form of sustainable agriculture and was an opening for the organic farming movement (Heckman, 2012). In similarity to this traditional agricultural system, modern agriculture use of commercial nitrogen-phosphorus-potassium fertilizers has mostly replaced compost and other organic amendments. Furthermore, the majority of commercial fertilizers contain small amounts or no content of silicon.

Source: http://www.carbonrootsinternational.org/biochar/

     For the reason that uptake of silicon is relatively large for many crops, a failure to return organic waste materials to farmland contributes to reduction of plant-available silicon from soil. An enrichment of biological activity in compost-amended soils may also have a role in mobilizing silicon for plant uptake. As an outcome of these significant changes in soil fertility management, there are good reasons to pay attention on the role silicon in soil fertility (Heckman, 2012). 

      Findings from over a decade of field trials conducted on the silicon research plots at Rutgers University, New Jersey Agriculture Experiment Station show that calcium silicate slag is an effective liming material and silicon fertilizer. Plants grown on calcium silicate slag amended soil exhibited increased silicon uptake.
Source: http://njaes.rutgers.edu/pubs/soilprofile/sp-v20.pdf

     
      Rice-husk biochar has high silica (SiO2) contents and silicon (Si) is a beneficial element for plant growth that helps plants overcome multiple stresses including biotic and abiotic stresses. Silicon plays an important role in increasing plant resistance to pathogens such as blast on rice (Datnoff et al., 1997) and powdery mildew on cucumbers (Miyake and Takahashi 1982a). Silicon is effective in preventing rice lodging by increasing culm wall thickness and vascular bundle size (Shimoyama, 1958), thereby enhancing stem strength. Silicon alleviates the effects biotic and abiotic stresses including salt stress, metal toxicity, drought stress, radiation damage, nutrient imbalance, high temperature, and freezing (Epstein, 1999; Ma and Tahakashi, 2002) and has various beneficial effects on plant growth and productivity (Ma and Tahakashi, 2002). Maize takes up Si actively from the roots (Liang et al., 2006).

Silicon vrs. Control

Powdery mildew lesions on wheat foliage were 44% less and yields were 10% greater in silicon amended plots. Source: http://njaes.rutgers.edu/pubs/soilprofile/sp-v20.pdf

     However, agronomists and farmers are not always aware that they could be able to improve crop production with increased stress and disease resistance by adding up a source of available silicon to the soil.

Applications of rice husk biochar to crops

     
      The benefits of silicon in crop production may be manifested as healthier plants and higher yield with fewer applications of pesticides and other chemical products (Heckman, 2012). Still, reports on the Si effect of rice husk biochar on plant seed germination are scant.