Crop response to soils amended with biochar: expected benefits and unintended risks

Abstract

Biochar (BC) from biomass waste pyrolysis has been widely studied due to its ability to increase carbon sequestration, reduce greenhouse gas emissions, and enhance both crop growth and soil quality. This review summarises the current knowledge of BC production, characterisation, and types, with a focus on its positive effects on crop yield and soil properties vs the unintended risks associated with these effects. Biochar-amended soils enhance crop growth and yield via several mechanisms: expanded plant nutrient and water availability through increased use efficiencies, improved soil quality, and suppression of soil and plant diseases. Yield response to BC has been shown to be more evident in acidic and sandy soils than in alkaline and fine-textured soils. Biochar composition and properties vary considerably with feedstock and pyrolysis conditions so much that its concentrations of toxic compounds and heavy metals can negatively impact crop and soil health. Consequently, more small-scale and greenhouse-sited studies are in process to investigate the role of BC/soil/crop types on crop growth, and the mechanisms by which they influence crop yield. Similarly, a need exists for long-term, field-scale studies on the effects (beneficial and harmful) of BC amendment on soil health and crop yields, so that production guidelines and quality standards may be developed for BCs derived from a range of feedstocks.

Biochar, Vermicompost, and Compost as Soil Organic Amendments: Influence on Growth Parameters, Nitrate and Chlorophyll Content of Swiss Chard (Beta vulgaris L. var. cycla)

“…The effects of their addition to agricultural soils depend on a number of factors, including feedstock properties and processing conditions, application rate, soil type, environmental conditions, and crop species [22,23]. About the latter, the yield response to compost or biochar applications are often contrasting; generally, either positive or negative and sometimes also neutral effects on crop yield and quality have been reported [13,24]. In Swiss chard, Paredes et al [25] found no significant differences on plant growth and yield comparing inorganic fertilizer and two doses of compost from olive mill wastewater; while other authors using a vermicompost mixed with coir for container-grown plants [26] or compost from organic domestic wastes and crop residues [27] observed higher growth and yield increases.…”

Biochar Mitigates Greenhouse Gas Emissions from an Acidic Tea Soil

“…Biochar amendment to a field, always with high pH and rich carbon content, has been well reported as an effective management strategy to counteract soil acidification for sustainable agriculture while reducing soil GHG emissions [15][16][17][18][19][20][21]. Biochar plays an important role in accommodating soil processes (e.g., soil nitrification, denitrification and organic matter mineralization), thus it affects soil C and N cycling [22].…”

Biochar-Ca and Biochar-Al/-Fe-Mediated Phosphate Exchange Capacity are Main Drivers of the Different Biochar Effects on Plants in Acidic and Alkaline Soils

“…Moreover, the dominant element content in biochar was Ca, as revealed by the ICP-OES analysis (Table 2). This fact confers to biochar an evident liming potential [2,27]. This effect, as well as the effects of crop P-use efficiency, has been described in many studies [17,18].…”

“…In these soils, fertility is improved in comparison to adjacent soils, which have had no organic C added. Similarly, biochar has been extensively applied as an amendment to fields to increase the organic C content as well as the C sequestration level in soils [2]. Biochar technology, either in production or agronomic, from an environmental point of view, has been extensively investigated [3].…”

“…The biochar use might be considered notable in comparison to the well-known humic and composted material applications as soil improvers or fertilization enhancers [6,7]. Although biochar application is widespread, some authors have shown an improvement in crop yields for acidic soils, but the opposite for alkaline soils [2,8]. One explanation of this loss of fertilization capacity of biochar in comparison to terra preta could be the lower Pi content of biochar in comparison to that of terra preta, which is assumed to originate from "Ash from fires, bones from fish and game animals, feces, urine, and turtle shells account for the relatively high levels of phosphorus in black earth" [9].…”