The effects of biochar on soil mineral availability

Abstract

Biochar is an organic soil amendment, produced by treating biomass feedstock at several pyrolytic temperatures and applied pressures in an oxygen limited environment. It is considered as a renewable resource that can be used to mitigate problems concerning both soil fertility and environmental issues. Biochar has several beneficial properties to enhance soil fertility, mainly by improving its water-holding capacity, aeration conditions, aggregate formation, pH, SOM and CEC while enhancing the nutrients availability, crop yields and microorganisms’ activity. This study investigated the effects of 3 different biochar amendments (10 Mgha-1, 50 Mgha-1 & 100 Mgha-1) together with a non-biochar control in 2 different soils (Luvisol & Calcisol) present in Malta, in which Lactuca sativa was cultivated in pots in a greenhouse experimental setup for 7 weeks. The key findings of the study demonstrated that Lactuca sativa crops grown in biochar amended soils contained more H2O but lower nutrients quantity than the plants grown in the controls. Both the height and width of lettuce exhibited no substantial differences but the root length in the 3 biochar amended Luvisol and Calcisol soil groups measured a greater length when compared with their respective control. The lowest sap NO3- content in both soil types was recorded in both controls, exhibiting a significant difference (P =<0.001) in the 3 lettuce groups in Luvisol soil but no substantial difference in Calcisol soil when compared with their control. Moreover, the sap PO4³⁻ content showed no significant difference between the lettuce groups. The level of absorbed Ba, Fe, Pb Mn, Cu, Sr and Cr showed similar results since their content recorded overall higher values in the control of both soil types. The Ni content uptake was very similar amongst the 4 different lettuce groups in each soil type while Zn uptake exhibited higher quantities than their respective controls except in the Calcisol soil with 10 Mgha-1 of biochar. In the Luvisol soil, the lowest drain water NO3- content, pH and EC were recorded in the control, while in the Calcisol soil, the lowest drain water NO3- content was recorded in the 100 Mgha-1 of biochar criterion and the lowest EC and the highest pH were measured in the control. With regards to post-harvest soil analysis, the control in Luvisol soil obtained the highest NO3- content and the lowest pH and EC measurements with no significant difference in the 3 parameters tested, whereas the lowest NO3- content, pH and EC were attained in the control of Calcisol soil. The obtained results showed that although biochar was amended to 2 calcareous and alkaline soils, some of the parameters analysed showed different results from one another, possibly due to differences in soil properties such as OM content, clay content, changes in soil pH, CaCO3 content, water holding capacity, dissolved organic C and also microbial biomass carbon.