Physicochemical Properties of Biochar Derived from Agricultural and Forestry Processing Wastes as Cultural Medium Substance and Its Effect on Growth Quality of Vegetable Plug Seedlings

Abstract

This study used biochar derived from agricultural and forestry processing wastes as a portion of culture medium to investigate its effect on the growth quality of vegetable plug seedlings. The yield of biochars was 31.02–89.02%, the content of element C was 18.94–85.79%, the Japanese cedar sawdust biochar (JCSBC) had the highest content, followed by the sorghum distillery residue biochar (SDRBC). The SDRBC had higher N content (6.46–11.73%), and its pH, iodine value, and electrical conductivity (EC) were 6.53–8.74, 71.01–210.33 mg/g, and 0.10–0.37 ds/m. The FTIR results of the SDRBC and cultivation waste bag biochar (CWBBC) in the spectrum had more C–H stretching vibration hydrophilic functional groups at 2875 cm–1 and 2995 cm–1 than these of JCSBC or pulp sludge biochar (PSBC). The air–filled porosity, container capacity, and total porosity of the culture medium with biochar were 9.71–13.79%, 61.27–63.11%, and 70.02–74.01%. The pH was 6.34–6.87, and the EC was 0.96–1.22 ds/m, approaching the requirements for general perfect medium. According to the growth quality results of Cucumis sativus plug seedlings, on Day 28 after seeding, the seedling index I and II of the peat with perlite were 0.1379 and 0.2790, respectively; both with SDRBC were the highest at the carbonization temperature of 450ºC (SDRBC–450), which were 0.1654 and 0.3376, significantly different from the peat with perlite and other biochar media. Moreover, because the SDRBC–450 had higher cation exchange capacity (CEC) than the others in day of seedling period during cultivation, the vegetable plug seedlings had better growth quality.