Does biochar improve soil water retention? A systematic review and meta-analysis

Biochar Amendment Enhances Water Retention in a Tropical Sandy Soil

“…The incorporation of biochar decreased the soil bulk density in the studied soil, as consistently reported in the literature [19,36,37]. In sandy soils, the bulk density tends to be more responsive to biochar application when compared to loamy soils [19], due to soil intrinsic properties, such as lower total porosity and high mineral particle density. The incorporation of biochar, a material with lower particle density than soil [21] decreased the bulk density of the soil by occupying volume and reducing total weight.…”

“…All of the biochar-amended soils held higher water content in the tensions between field capacity and the permanent wilting point (Figure 2) as compared to the control, increasing AWC to be potentially used by plants [52]. The increases in AWC that were found in this study fall within the range reported by Razzaghi et al [19], being observed in 57 studies that were conducted in coarse-textured soils around the world. However, biochar addition did not have the expected linear effect, which suggested that the highest rate used was excessive for this short-term study.…”

“…However, under higher tensions, water is retained in micropores and it cannot be drained by gravity. The increase in microporosity due to biochar amendment leads to a greater water volume retained in the soil at these tensions [50], up to the wilting point [19]. The water might be directly stored in internal biochar micropores [19], or, as Petersen et al [51] reported, in drainage pores converted by biochar particles into smaller water-holding pores.…”

“…The increase in microporosity due to biochar amendment leads to a greater water volume retained in the soil at these tensions [50], up to the wilting point [19]. The water might be directly stored in internal biochar micropores [19], or, as Petersen et al [51] reported, in drainage pores converted by biochar particles into smaller water-holding pores. All of the biochar-amended soils held higher water content in the tensions between field capacity and the permanent wilting point (Figure 2) as compared to the control, increasing AWC to be potentially used by plants [52].…”

“…These benefits include increasing soil pH [14], cycling and plant-availability of nutrients [15], cation exchange capacity [16], 2 of 13 adsorption of potentially toxic elements [17], and microbial biodiversity [18]. In addition, a recent global meta-analysis showed the potential of biochar use for enhancing soil physical properties, such as reducing bulk density and increasing water retention capacity [19], especially in coarse-textured soils under temperate climate [20][21][22]. However, there is a paucity of studies investigating the potential of biochar to increase water retention capacity in tropical soils [23][24][25] and particularly, in sandy soils, where plants are more susceptible to water stress.…”