Pyrolytic biochars from sunflower seed shells, peanut shells and Spirulina algae: their potential as soil amendment and natural growth regulators

Abstract

Several studies have shown that pyrolysis conditions and feedstocks are the key factors influencing biochar chemical and physical properties. The information on the nature of biochar is quite important, especially when this carbonaceous material is intended to be used as a potential soil amendment. In this study, we investigated the formation and characterisation of biochars produced from vacuum pyrolysis of sunflower seed shells (SSS), peanut shells (PS) and Spirulina algae (Sp) at 280 °C (for SSS, PS and Sp) and 350 °C (for PS). As a proxy to test the potential of each biochar as soil amendment, we assessed the germination and growth effects of the biochar water-extractable substances (BWES) at different concentrations (10; 7.5; 5; and 2.5% w/v) on Lactuca sativa. Results showed that the biochar from pyrolysis of PS at 280 °C would be the most suitable soil amendment, since its BWES did not affect germination and exhibited a remarkable growth-promoting effect (50-100%) on roots and stems of L. sativa. In contrast, BWES from SSS, Sp and certain concentrations of PS produced at 350 °C inhibited growth of Lactuca sativa, and particularly BWES of Spirulina dramatically reduced germination, posing a risk for direct application as soil amendment. The presence of carbonyl derivatives in the BWES from PS may be linked to the stimulatory effects of this extract. Aromatics could be responsible for the germination and growth inhibition in the BWES of SSS, while nitrogen organic compounds would enhance the inhibitory effect in BWES from Sp.

Unlocking the Potential of Agrifood Waste for Sustainable Innovation in Agriculture

“…In this sense, biochar from sunflower seed shells, peanut shells and Spirulina algae were tested separately in lettuce. The results showed that when peanut shells were used (pyrolysis at 280 • C) it did not affect germination and exhibited a remarkable growthpromoting effect on the roots and stems of lettuce, as the presence of carbonyl derivatives and aromatics in the water-extractable substances of peanut shell biochar may be linked to the stimulating effects of this extract [87]. In contrast, the water-extractable substances from the biochar of both bio-waste produced at 350 • C inhibited the growth of lettuce, posing a risk of direct application as soil amendment.…”

“…In contrast, the water-extractable substances from the biochar of both bio-waste produced at 350 • C inhibited the growth of lettuce, posing a risk of direct application as soil amendment. In this case, aromatics may be responsible for growth inhibition in the water-extractable substances of the biochar from the sunflower seed shells, while the organic nitrogen compounds would enhance the inhibitory effect in the water-extractable substances of the biochar of the Spirulina algae [87].…”

Properties of Biochar Derived from Tea Waste as an Alternative Fuel and Its Effect on Phytotoxicity of Seed Germination for Soil Applications

“…Root lengths were also measured for each sample. A germination index of at least 50% is required for use in the soil [43]. A seed was considered physiologically germinated if the radicle was longer than 2 mm.…”

Recent advancements in biochar production according to feedstock classification, pyrolysis conditions, and applications: A review

“…In addition, different pyrolysis types for biochar production from algal biomass were investigated. Silva et al (2020) produced biochar with 43% yield by fast pyrolysis (residence time: 1 min) of Spirulina (blue green micro-algae grown in alkaline water) at 280 C. A yield of biochar from fast pyrolysis (43%) was obtained more than that of slow pyrolysis (36%).…”