Abstract
Biochars have long been associated with elevating plant productivity. An increasing number of studies, however, report that char application might also impair plant nutrient availability and reduce yields. In particular, char accompanying compounds as well as a hypothesized immobilization of nitrogen have been identified as playing a significant role in possibly diminishing plant productivity following char application. Herein, we tested the fertilizing effects of modified biochars in order to derive knowledge required to develop tailor-made chars, which predictably affect plant nutrition. Slow-pyrolysis maize cob biochar was modified by washing with either ethanol or hydrochloric acid to remove ash and organic compounds or by loading it with nutrient-rich residues in the form of digestate from the bioenergy sector. Maize plants were grown for 35 days on biochar-amended sand. We analyzed both substrate properties (pH, total carbon, and nitrogen, available magnesium and potassium) and plant functional traits (biomass, leaf area, root to shoot ratio, specific leaf area). Our results suggest that total plant biomass production remained unaffected by the application of biochar and its washed forms. Contrastingly, nutrient-loaded biochar induced a significant increase in productivity at similar nutrient levels due to improved plant nutrient uptake. Further research is required to understand the role of biochar modifications that facilitated improvements in plant productivity.
Highlights
Biochar is the porous, poly-aromatic product of an incomplete thermochemical conversion of organic biomass, which is increasingly used as a soil amendment [1] to increase crop yields [2,3].depending on the chars’ physical and chemical properties their impact on plant productivity remains largely unpredictable due to complex interactions between soil and environment [4,5,6]
Results of this study suggested that digestate application has positive fertilization effects in low-fertility substrates, similar to mineral fertilizer, even though digestate application may have a negative impact on the permeability in sandy substrates that could interfere with germination
While results of other studies and meta-analyses reported that plant productivity may remain unaffected after biochar application [2,4,8], untreated biochar addition as used in our study resulted in a biomass increase of 10% compared with the pure sand substrate, which is in line with previous results of a meta-analysis by Jeffrey et al [41]
Summary
Poly-aromatic product of an incomplete thermochemical conversion of organic biomass, which is increasingly used as a soil amendment [1] to increase crop yields [2,3].depending on the chars’ physical and chemical properties their impact on plant productivity remains largely unpredictable due to complex interactions between soil and environment [4,5,6]. Poly-aromatic product of an incomplete thermochemical conversion of organic biomass, which is increasingly used as a soil amendment [1] to increase crop yields [2,3]. Agronomy 2020, 10, 567 of plants in biochar amended soils varies due to accompanying organic and inorganic compounds that might affect germination and plant nutrition negatively [6,8,9,10]. Modification techniques include (i) chemical (e.g., amination, coatings, loadings), (ii) physical (e.g., steam activation), and (iii) biological (e.g., composting) modifications to increase the biochars’ sorption capacity, modify porosity, load them with nutrients or remove superfluous compounds [13,14,15,16,17]
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