Abstract
Thermal biomass transformation products are considered to be one of the
best materials for improving soil properties. The use of cavitated
charcoal is not described in the literature. The study was carried out
with 10% aqueous charcoal mixture that were introduced into loamy sand
and clay at rates of 1.76%, 3.5%, 7.0%, and 14.0%. The application
of cavitated charcoal reduced the acidification of both soils. The
highest introduction rate of the material (14.0%) increased the content
of total carbon (CTot) by 197% in
the loamy sand and by 19% in the
clay compared to that in the control treatments. The application of
cavitated charcoal did not significantly change the total content of
heavy metals. The effect of the application of cavitated charcoal on the
bioavailability of heavy metals was tested after extracting the most
mobile forms of Cu, Cd, Pb, and Zn with a 0.01 mol
dm-3 solution of CaCl2. Regardless of
the element and the soil used, the application of cavitated charcoal
reduced the content of the CaCl2-extracted forms of
heavy metals. Following the application of cavitated charcoal, the loamy
sand soil presented an even lower content of the most mobile forms of
the studied elements. It should also be noted that regardless of the
soil texture, mobile forms of the elements decreased with the increased
cavitated charcoal rate. The respiratory activity values of the soils
into which cavitated charcoal was introduced were low, which indicates a
large number of dormant microorganisms. Additionally, the results of
dehydrogenase and urease activity indicated the low metabolic activity
of the microbial population in the soils, especially with the relatively
high rates (7.0% and 14.0%) of cavitated charcoal. However, the
cavitated charcoal used in the study showed a significant, positive
effect on the amount of biomass Sorghum saccharatum (L.), and its
application significantly reduced the heavy metal content in the biomass
of Sorghum saccharatum (L.).
Keywords: cavitation, charcoal, soil, enzymatic activity,
plant, heavy metals
1. Introduction
The appropriate use of waste biomass is one of the ways to achieve
sustainable agriculture in the 21st century. This
approach will help create a product capable of improving soil
characteristics in terms of its chemical and biological properties, as
well as the quantity and chemistry of obtained plant biomass (Glaser,
2007). Significant amounts of waste biomass are generated in the world,
and the instability of this waste makes its transformation often a key
problem for the environment. The product of thermal biomass
transformation is charcoal with properties similar to biochar. Solid
products of thermal biomass transformation, due to their multiple
specific properties, are often referred to as environmentally friendly
materials (Deenik et al., 2010; Oliveira et al., 2017). The beneficial
effects of these materials on soil water retention capacity, cation
exchange capacity, and improvement of soil function as a carbon
reservoir is noted here because of the high C content in these
environmentally friendly materials and their resistance to microbial
degradation (Cheng et al., 2008; Tan et al., 2017). Despite many studies
on the effect of charcoal and biochar on the environment, it was not
possible to clearly define the mechanisms of their action
(Dieguez-Alonso et al., 2018). The increased number of tests carried out
have proven that the effect of thermally transformed organic materials
on soil and plant properties is varied. Their effect is also conditioned
by, among others, the type of feedstock, production conditions, material
rate, location of tests and type of plant cultivated (Deenik et al.,
2010; O’Connor et al., 2018). Deenik et al. (2010) demonstrated that the
independent application of thermally transformed organic materials
worsened the conditions for plant growth and development, probably due
to limited nitrogen access and stimulation of soil microorganismal
growth. The study of Kloss et al. (2013) indicated a similar plant
response, especially in the first two years after the application of
biochar. In addition, these authors noted a decrease in the content of
some trace elements in plant biomass. According to Kloss et al. (2013),
even with additional mineral fertilisation, the use of thermally
transformed organic materials creates the risk of a short-term reduction
in plant growth and development.
Previous studies on charcoal and biochar were focused not only on
determining the structure and chemistry of these materials but also on
searching for new solutions aimed at enriching them with various
components and modifying their production process (Jassal et al., 2015;
Gondek et al., 2018). Given the properties of charcoal and the way it is
applied, as well as the resulting environmental problems, there is a
need to identify alternative production methods (form) or preparations
for use (Montanarella and Lugato, 2013). Due to the nature of the
cavitation process, it is possible to homogenise cavitated material with
the implosion of gas bubbles. In the case of hydrodynamic and acoustic
cavitation, cavitation bubbles are present in liquid as a result of
local ruptures of the continuous medium caused by high tensile forces.
These forces arise from local sudden pressure decreases that may occur
either in hydrodynamic processes or in a high-intensity ultrasonic field
(20 kHz – 1 MHz) (Lenik and Ozonek, 2012). The cavitation process can
be modified by adding various types of chemical substances or by
changing the physical parameters of the process (Nakashima et al.,
2016).
The aim of the study was to assess the effect of charcoal after
cavitation on the chemical and biochemical properties of soil, as well
as on the quantity and chemistry of Sorghum saccharatum (L.)
biomass.