Enhancing cation exchange capacity of weathered soils using biochar: feedstock, pyrolysis conditions and addition rate

Authors: DOMINGUES, RIMENA - University Of Minnesota; SANCHEZ-MONEDERO, MIGUEL - Centro De Edafología Y Biología Aplicada Del Segura-Csic; Spokas, Kurt; MELO, LEONIDAS - Federal University Of Lavras; TRUGILHO, PAULO - Federal University Of Lavras; VALENCIANO, MURILO - Federal University Of Lavras; SILVA, CARLOS - Universidade De Sao Paulo

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2020
Publication Date: 6/11/2020
Citation: Domingues, R.R., Sanchez-Monedero, M.A., Spokas, K.A., Melo, L.C., Trugilho, P.F., Valenciano, M.N., Silva, C.A. 2020. Enhancing cation exchange capacity of weathered soils using biochar: feedstock, pyrolysis conditions and addition rate. Agronomy. 10(6):824. https://doi.org/10.3390/agronomy10060824.
DOI: https://doi.org/10.3390/agronomy10060824

Interpretive Summary: The ability to increase the nutrient holding capacity of soils is an important mechanism to improve the fertility of low productivity soils, particularly those located in humid and tropical regions. In this study, we observed the impact of three different feedstocks that were used for biochar production at three different temperatures (350, 450, and 750 C) and examined the impacted on selected soil properties. Feedstock, pyrolysis temperature and application rate were key factors controlling the cation exchange capacity (CEC) of biochar-amended soils and increasing the fertility of the two Oxisols used in this study. High-ash biochar produced at low pyrolysis temperatures (=450 C) increases the soil CEC to the greatest extent. Interestingly, increases in soil CEC from biochar additions correlated with soil pH rather than to soil carbon. CEC of the amended soils can be estimated from the biochar CEC, rate, liming value and the extent of soil acidity neutralization. In this short-term incubation study, aging is a minor factor controlling CEC of the biochar-treated soils. Overall, this study provides results that guide selecting biochars for specific agronomic and environmental applications, such as improving soil CEC. These results are significant to assist scientists, engineers, farmers, and supplying guidance for improving soil productivity with biochar additions as well as simultaneously sequestering carbon.

Technical Abstract: The addition of alkaline and high-cation exchange capacity (CEC) biochars is a suitable strategy to increase the CEC of weathered soils. The aim of this study was to evaluate the effect of biochar from different feedstocks and pyrolysis temperatures on the CEC of two contrasting Oxisols. Biochars produced from chicken manure (CM), eucalyptus sawdust (ES), coffee husk (CH) and sugarcane bagasse (SB), plus a control (without biochar), at 350, 450, and 750 'C were mixed with the soils at 2; 5; 10 and 20% (w/w) and incubated for 9 months. Feedstock, pyrolysis temperature and addition rate of biochar were key factors controlling the alteration of soil CEC. The CH biochar pyrolyzed at 350 'C was the most effective matrix at increasing soil CEC. In a rate-dependent way, ES and SB biochars increased C contents of both soils without improving soil CEC. The efficiency of high-ash biochars in enhancing soil CEC in both Oxisols was limited by the alkalization caused by high rates of CH and CM biochars. The increase in CEC is soil-dependent and modulated by high-ash biochar CEC and application rate, as well as by the original soil CEC.