Biochar is the charcoal obtained by the pyrolysis of biomass, i.e.,by incomplete thermal decomposition of organic material underlow oxygen conditions at relatively low temperatures (<700 C).Unlike charcoal and similar materials, biochar is produced with theaim of being used as a soil amendment (Lehmann and Joseph,2009). However, biochar is a more stable solid than the commonorganic conditioners, due to its very low degradation rate which isestimated as several hundred years for total degradation. Thus, itspotential effects on the chemical, physical and biological propertiesof the soil may extend over a long period of time (Atkinsonet al., 2010). Most of the available studies focus on the biochemicaleffects of biochar on amended soil, including the nutrients that itmakes available, as well as on its impact on CEC, pH, vegetativegrowth, crop yield, and its C sequestration potential (Atkinsonet al., 2010; Mukherjee and Lal, 2013). However, the incorporationinto the soil may modify the physical and hydraulic properties ofthe porous medium, such as bulk density, water retention,hydraulic conductivity, porosity and penetration resistance. Thisis mainly due to both its highly porous structure and the exposedsurface area (Lehmann and Joseph, 2009). In general, some* improvements have been reported both for medium-coarsetextured soils (e.g., Uzoma et al., 2011a) and forfine textured ones(e.g., Kameyama et al., 2012) but, as one can imagine, they arebiochar and soil-specific (Mukherjee and Lal, 2013). However, todate, little attention has been paid to investigating the biocharinducedchanges on physical and hydraulic properties offinetextured soils. Kameyama et al. (2012), performed laboratoryexperiments on the saturated (Ks) and unsaturated (K(h)) hydraulicconductivity on a sieved and repacked clay soil. They observed thatKs increased significantly only for the higher concentrations ofbiochar, while no differences were detected for K(h). Althoughthese results probably cannot be extended tofield conditions (dueto the non-comparable characteristics of soil structure and soilporosity), the authors concluded that the amended soils might beinfluenced by changes in soil porosity as well as by the continuity,shape and tortuosity of the conducting soil pores. However, Asaiet al. (2009) found no significant differences in Ks measurementswhen using relatively similar amounts of amendments(Kameyama et al., 2012). Conversely, the effects of biochar additionon soil water retention or on soil bulk density seem to be lessquestionable. For example, Kameyama et al. (2012) reported thatthe volumetric water content for a given pressure head valueincreased as the concentration of the amendment increased. Sunand Lu (2013) found similar behavior in another clay soil. They alsoreported that there were significant increases in saturated soilwater content, due to greater amounts of water being held bothinside the biochar pores and between the biochar particles. Theeffects of amendments on soil bulk density are also quite clear. Dueto its very low density, it has been reported that adding biocharleads to a decrease in soil bulk density (Haefele et al., 2011).However, although this was clearly evident during afieldexperiment, the authors stated that the effect was already notsignificant in the second season after application, and becamenegligible in the following seasons, which suggests that the effecton soil bulk density is transient (Haefele et al., 2011). In otherwords, since biochar may affect the main physical and hydraulicproperties of the porous media it is desirable that, for a given soil,the biochar-induced changes (i.e., for different levels of amendments)can be assessed simultaneously.Several studies have been carried out throughout the world toidentify the effects of incorporating organic matter into the soil,and the resulting advantages for its physical and hydraulicproperties are well known (Castellini et al., 2014). In recent yearsthere has been increased use of biochar as an addition toagricultural soils, since it is seen as potentially improving bothcrop productivity and soil quality (Vaccari et al., 2011; Baronti et al.,2014). It is an alternative that may be potentially integrated intosustainable agricultural systems, especially those in the clayeysoils of Southern Italy (Castellini et al., 2014). However, an accurateevaluation of the biochar effects on the physical and hydraulicproperties of the soil is needed, since the effects of excessively highinputs are difficult to remedy. There is only very limitedinformation available on its impact on the hydraulic conductivity(Asai et al., 2009; Kameyama et al., 2012; Barnes et al., 2014), thewater retention (Sun and Lu, 2013; Kameyama et al., 2012) and thedry bulk density (Haefele et al., 2011; Barnes et al., 2014) of clayeysoils, and further research is necessary.The main objective of this paper was to evaluate the impact ofbiochar additions on the physical and hydraulic properties of a claysoil. The effects on saturated and unsaturated hydraulic conductivity,water retention, capacitive indicators and dry bulk density ofthe soil should be evaluated, and factors that could have affectedthe measurements should be considered. Biochar effects onsimulated durum wheat yields should also be evaluated.
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