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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.

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This study investigated the amendment of sugarcane bagasse biochar (SCBB) on soil fertility, crop yield, and nutrient loss in two different-textured soils under sugarcane (Saccharum spp.) production. Eleven megagrams per hectare of freshly incorporated biochar increased yield of plant cane by 22% in light-texture soil (LS) and 12% in heavy-textured soil (HS). Although the overall yield of the ratoon crop was lower, the biochar treatment produced 20 and 14% higher yields than the control at the LS and HS sites, respectively. Biochar increased soil carbon (C soil ) across LS and HS sites by 15% and decreased the soil C/N ratio by 19%. Over the two growing seasons and sites, cumulative runoff volume, and loads of NO 3 --N, PO 4 -3 -P, biological oxygen demand (BOD 5 ), total organic C (TOC), and total suspended solids (TSS) were reduced by 33, 35, 39, 25, 24, and 54% with biochar. Calcium and K losses in runoff were also reduced by 43 and 24% with biochar. It reduced NH 4 + -N leaching in LS and HS soils over the two growing seasons by 33-167% and 66-81%, respectively, and reduced PO 4 -3 -P leaching by 45-57% in HS over 2 yr. Although biochar is not considered a fertilizer, SCBB acted as a source of nutrients, increasing soil fertility and crop yield. It also reduced nutrient losses during heavy rain events typical of the subtropical climate of Louisiana. 1 INTRODUCTION Sugarcane(Saccharum spp.) is one of the major crops in Louisiana, the second largest producer of sugarcane in the United States (Viator et al., 2019). Harvest sugarcane gen-Abbreviations: BOD 5 , biological oxygen demand; CEC, cation exchange capacity; DIW, deionized water; EC, electrical conductivity; HS, heavy-textured soil; ICP-OES, inductively coupled plasma-optical emission spectroscopy; LS, light-textured soil; SCBB, sugarcane bagasse biochar; TOC, total organic carbon; TSS, total suspended solidsThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.