Feedstock type and pyrolysis temperatures regulate the impact of biochar on soil health in arid land agroecosystems

Biochar amendments are gaining globally for improving soil health and carbon storage. This study investigated the physicochemical properties and impact on soil microbes of biochar amendments derived from two feedstock sources: date palm leaves (D), and mesquite plants (M); pyrolyzed at 450, 600 and 750 ℃. SEM images revealed that the pore size increased with increasing pyrolysis temperature. According to the Fourier transform infrared spectroscopy results, the increase in pyrolysis temperatures reduced the O-H and C-O bonds while increasing the proportion of C-C bonds. The dynamic thermal gravimetric analysis evidence that the thermostability was greatest at a pyrolysis temperature of 750 °C, and was also significantly different for the two feedstock materials used. The M feedstock produced biochar with the highest surface area (600 m2 g-1) and carbon content based on loss on ignition (95%); moreover, this biochar reduced soil microbial enumeration and respiration, and this effect was more pronounced for biochar pyrolysed at 750 °C. As a result, M biochar feedstocks are not recommended for improving soil health, but they may be useful as microbial inhibitors when soil-borne plant pathogens are present. Based on the physicochemical properties and the biochar impact on soil properties, D at 600 °C was chosen as the best-performing biochar in our study for improving soil health in arid lands and was selected for further research as a soil amendment. The large differences in biochar physicochemical properties and their observed effect on soil properties confirmed that the feedstock type and pyrolysis temperatures must be considered during biochar production for soil health applications in arid-land agroecosystems.