Cassava's harvest residue biochar from rotary kiln pyrolysis: Effects on sandy loam soil properties and maize growth

Cassava shoot system (CSS) biomass is a smart and despised raw material for biochar production. Commonly, cassava roots and their husk are most exploited as feedstock for the thermoconversion process. In this research, we proposed the production of biochar from CSS in a continuous pyrolysis reactor at temperatures of 400 °C, 500 °C, and 600 °C, searching for added value to this agricultural residue and to produce a soil amendment material with good water retention potential. CSS-biochars have their effects tested on sandy loam soil at 25- and 50-ton ha⁻¹ application rates. Considering soil amendment and carbon sequestration purposes of biochars, the volatile matter, fixed carbon, and ash content are important parameters to be considered. Higher temperature produces more stable and less organic functionalized biochars, measured by the O/C values from 0.21 to 0.03 and H/C from 0.96 to 0.46. Biochars’ pH increases directly with the ash content and significantly alters the soil pH, increasing it from 5.0 to 6.0 with BC500C and BC600C at a rate of 50 tons ha⁻¹. At the same application rate, BC400C and BC600C presented an increase in water-holding capacity of 13 % and 20 % compared with the control sample, respectively. Overall, the matric potential view for all application rates only the CSS-biochar produced at 600 °C demonstrated superior water retention compared to the reference control. An important observed aspect is the no significant impact of biochar on the maize germination step in pot experiments.