**4. Conclusions**

*Applications of Biochar for Environmental Safety*

It was reported that incorporation of biochar into salt-affected soil could alleviate salinity stress in potatoes [48] mainly because of its high salt (Na<sup>+</sup>

adsorption potential. In another study, Akhtar et al. [53] examined the effect of different levels of salinity and biochar on wheat yield. The results showed that biochar application positively influenced growth and yield of wheat under saline condition. However, Thomas et al. [28] noticed high salt adsorption potential of biochar, some studies have reported negative effect of biochar on crop productiv-

Biochar could improve the soil physicochemical and biological properties under conditions of abiotic stresses [55]. Biochar poultry manure compost (BPC) with pyroligneous solution (PS) in the saline soil increased microbial biomass carbon and the activities of urease, invertase, and phosphatase in bulk soils and rhizosphere soils under maize cultivation, according to Lu et al. [56]. Similarly, Bhaduri et al. [57] concluded that the effects of biochar on soil enzyme activities in saline soil vary with the applied rate of biochar, incubation time, and soil enzyme types.

pH but increased the soil electrical conductivity as compared to the control [28]. Similarly, a biochar produced by furfural (a colorless liquid used in synthetic resin manufacture, originally obtained by distilling bran) in saline soil decreased pH, while increasing the soil organic carbon, cation exchange capacity (CEC), and

When applied in saline soils, composted biochar increased the soil organic matter content and CEC and decreased the exchangeable Na and soil pH [58]. These studies showed that biochar addition in saline soils could improve the plant growth

Corroborating [52], a study carried out by Lin et al. [62] reported that the biochar application in saline soil improved wheat and soybean yields by increasing the exchangeable K concentration (by 44% over control) and increasing the K/Na ratio in plants, improving plant salt tolerance. According to Lashari et al. [63], a considerable increase in K concentration and K/Na ratio in the leaf sap of corn under salt stress and an increasing supply of K were suggested as major mechanisms

The benefits of biochar in plant growth in saline soils observed in several studies

<sup>−</sup> and H2O2 concentration reduction in osmotic stress through

cited by Saifullah et al. [52] also include reduction in oxidation stress through

improving water holding capacity and thus availability of water; lower production of phytohormones; improvement in stomatal density and conductance; improvement in seed germination and the promotion of microbial activities; and a bacterial

Plants under salinity stress produce abscisic acid (ABA), and it is a good indicator of the osmotic stress, acting as a long-distance signal molecule to close stomata under water deficit conditions [64]. Thus, decreased production of ABA could be attributed to a biochar-induced improvement in water availability to plants, which would result ultimately in increased stomatal conductance. Further, enhanced availability of water and nutrients with biochar application under saline conditions

The accumulation of Na and impairment of K nutrition are major characteristics of salt-stressed plants [59]. Thus, improved K/Na ratio through enhancing K availability is considered a useful tool to increase plant growth and yield under saline soils [60, 61]. Biochar, depending upon feedstock, may increase K concentration in soils, and this increase in salt-affected soils counteracts the adverse impacts of Na, being considered one of the major benefits associated with biochar application in

by improving the soil biological activity and physicochemical properties.

ity, but these were generally restricted to specific type of biochar [54].

The biochar application in salt-stressed soil (30 g m<sup>−</sup><sup>2</sup>

responsible for the alleviation of salt stress to plants.

community shift toward the beneficial taxa in the rhizosphere.

available P in the soil [31].

saline soils [52].

degradation of O2

could improve seed germination.

)

) did not affect the soil

**198**

The interaction of biochar with soils with salinity conditions is essential for determining any contrasting effects, which also depend on the physicochemical properties of biochar and the raw material used for biochar production. Elucidating the effect of biochar type on plant growth and development and soil biochemical properties provides important guidance on the selection of feedstock type and production technology, which could be applied under specific environmental conditions.

Different methods of producing biochar from the same source play a critical role in the expression of soil ecological effects, which underpin the assumption of a link between chemical and physical properties of biochar and enhanced plant nutrient acquisition, symbiotic performance, and plant stress tolerance.

Although there is an increasing number of studies about biochar and its effects in saline soils for improvement of plant growth, the results obtained until the present are still not conclusive given the diversity of raw material and methods for biochar production. It is still necessary to conduct more investigations in order to better use biochar for ameliorating the adverse salinity effects in soils.
