Abstract
Recent studies have shown that silicon (Si) dissolution from biochar may be influenced by the pyrolysis temperature. In addition, the enhancement of biochar by treatment with alkali has been proposed to produce a Si source that can be used for environmentally friendly plant disease control. In this study, biochars from rice straw and rice husk pretreated with KOH, CaO and K2CO3 and then pyrolyzed at 350, 450 and 550 °C were prepared to evaluate the effects of pyrolysis temperature on Si release and plant uptake from alkali-enhanced Si-rich biochar. Extractable Si and dissolution Si from the prepared biochars were assessed by different short-term chemical methods and long-term (30-day) release in dilute acid and neutral salt solutions, respectively, along with a rice potting experiment in greenhouse. For both rice straw- and husk-derived alkali-enhanced biochars (RS-10KB and HS-10K2B, respectively), increasing the pyrolysis temperature from 350 to 550 °C generally had the highest extractable Si and increased Si content extracted by 5-day sodium carbonate and ammonium nitrate (5dSCAN) designated for fertilizer Si by 61–142%, whereas non-enhanced biochars had more extractable Si at 350 °C. The alkali-enhanced biochars produced at 550 °C pyrolysis temperature also released 82–172% and 27–79% more Si than that of 350 °C produced biochar in unbuffered weak acid and neutral salt solutions, respectively, over 30 days. In addition, alkali-enhanced biochars, especially that derived from rice husk at 550 °C facilitated 6–21% greater Si uptake by rice and 44–101% higher rice grain yields than lower temperature biochars, non-enhanced biochars, or conventional Si fertilizers (wollastonite and silicate calcium slag). Overall, this study demonstrated that 550 °C is more efficient than lower pyrolysis temperature for preparing alkali-enhanced biochar to improve Si release for plant growth.
Highlights
The beneficial effect of Si on plant growth has been well documented
The pH and ash content of alkali-enhanced rice straw and husk biochars increased with increasing pyrolysis temperature (Tables S1 and S2)
For the rice husk-derived biochar treatments, the Si uptake contents in straw associated with the RH-0B-550 and RH-10K2B-550 treatments were significantly higher than those of the corresponding RH-0B-350 and RH-10K2B-350 treatments by 9 and 33%, respectively. These results indicated that alkali-enhanced biochar Si sources prepared at high pyrolysis temperatures tended to promote higher Si uptake by rice straw, in the case of the rice husk-derived biochar products
Summary
The beneficial effect of Si on plant growth has been well documented. It includes improving plant resistance to pest and disease, enhancing mechanical strength, and decreasing nutrient imbalance, as well as alleviating metal toxicity and other stresses due to soil salinity, extreme temperatureCollege of Chemical and Environment Science, Shaanxi University of Technology, Hanzhong, Shaanxi 723001, ChinaSchool of Plant, Environmental and Soil Science, Louisiana State University, 104 Sturgis Hall, Baton Rouge, LA 70803, USACollege of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China and drought conditions (Meyer and Keeping 2001; Neumann and Zur 2001; Epstein 2009; Guntzer et al 2012; Adrees et al 2015; Islam et al 2020). The application of Si fertilizers to plants, especially Si-accumulators such as rice, maize, sugarcane, wheat, and ryegrass is necessary to ensure plant healthy growth. Several studies have shown that biochars produced by pyrolyzing Si-rich waste biomass could be used as bioavailable Si source to Siaccumulator plants (Houben et al 2014; Liu et al 2014; Li et al 2014, 2018; Abbas et al 2017; Linam et al 2021). Application of biochars significantly increased Si content in stem and blades of wheat, rice, and perennial ryegrass (Liu et al 2014; Abbas et al 2017; Wang et al 2018a, 2019a). Biochar could serve as a low-cost, renewable, and environmentally friendly Si source
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