Fodder radish seed cake biochar for soil amendment

Abstract

In this work, fodder radish seed cake (FRSC) was pyrolyzed in a rotary kiln reactor at 0, 3, and 6 rpm, at final temperature of 500 °C. Maximum biochar yield was observed at 0 rpm (≈ 26 wt.%). Increase of the rotary speed decreased the volatile matter content and increased the ash content of the biochars. Biochars exhibited alkaline pH (≈ 9.0), low electrical conductivity (< 105.6 dS m^-1), and high cation exchange capacity (69 to 78 cmol_c kg^-1), as well as high nitrogen contents (≈ 80 g kg^-1). FTIR analysis presented biochars with similar spectra, with carboxyl and carbonyl groups within the structure, along with aromatic rings and nitrogen containing functions (amides). Biochar incubation experiments in an acrisol at different biochar doses (5 g L^-1 soil to 40 g L^-1 soil) were performed in order to evaluate changes in soil fertility parameters caused by FRSC biochar application. Results indicated that most of macro (N, P, K, Ca, Mg) and micronutrients (S, Cu, Zn, Mn, B, Na) increased with increase of the dosage, along with the decrease in Al and H+ Al contents. An increase in pH (from 4.25 to 5.33) was also observed, in electric conductivity (from 30.0 to 45.7 dS m^-1), and a decrease in soil real density (from 3.67 to 2.99 kg L^-1) at the dosage of 40 g char L^-1 soil.

Keywords: Biochar; Fodder radish; Organic fertilization; Pyrolysis; Rotary kiln.