Abstract
Because of the low consistency of the results obtained in the field, the use of biochar as a soil amendment is controversial. Thus, in general, in acidic soils, results are positive, while in alkaline soils, they are non-significant or even negative. The results regarding biochar action in acidic soils have been related to a lime-like effect due to its alkaline pH and the high doses normally used. However, the causes of biochar effects in alkaline soils remain unknown. Our objective was to explore the chemical mechanism of biochar interaction in acidic and alkaline soils. We used well-characterized biochar as a component of two complex N and PK granulated fertilizers at two different doses (1% and 5%). These fertilizers were applied to wheat cultivated in pots containing an alkaline soil and grown for 60 days. No effect was shown for the N-biochar fertilizer application. However, the PK-biochar fertilizer application caused a decrease in crop yield. In addition, the adsorption isotherms of Al, Fe, Mo, Mn, and Phosphate (Pi) in biochar were also studied. The results showed that Fe and Al were rapidly adsorbed in biochar, while Pi was only adsorbed on the Fe-, Al-biochar complex. Desorption experiments showed that P and Fe/Al were not desorbed from the P-Fe/Al-biochar complex by water or the Olsen reagent, while partial desorption was observed when HCl 0.1 M was used. This blockage of Fe/Al and P through Fe/Al bridges in biochar could partially explain the negative effects in alkaline soils. After these studies, soil solution sorption experiments were carried out in both acidic and alkaline soils and were complemented with a greenhouse trial using tomato plants. The results showed that biochar enhanced foliar Ca and N content, as well as growth in acidic soil only, and the possible mechanism of the failure in alkaline soils.
Highlights
Amazonian terra preta soils have been the inspiration of biochar addition to soils [1]
We studied the effects of fertilizers granulated incorporating biochar [18,21] at different concentrations, as well as of biochar used as an amendment, on plant growth and mineral nutrition
This study showed that the effects of biochar on soil properties and plant growth were greatly influenced by its capacity to bind Fe and Al, as well as Pi through Fe and Al chemical bridges
Summary
Amazonian terra preta soils have been the inspiration of biochar addition to soils [1]. In these soils, fertility is improved in comparison to adjacent soils, which have had no organic C added. Either in production or agronomic, from an environmental point of view, has been extensively investigated [3]. Agronomic yields results in crops treated with biochar amendments are controversial [4,5]. More controversial are its collateral effects on decreasing soil microbial biomass, influencing soil physical properties or processes affecting the mobility and loss of biochar in the soil profile, or influencing soil organic matter dynamics [4]. The biochar use might be considered notable in comparison to the well-known humic
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