addition on saturated (Kfs) and
unsaturated (K(h)) hydraulic conductivity, water retention, capacitive indicators such as macroporosity
(Pmac), air capacity (AC), plant available water (PAWC) and relative
field capacity (RFC, equal to the ratio
between
field capacity and saturated soil water content), dry bulk density (rb) of a repacked clay soil.
Biochar effects on simulated wheat yields were also evaluated using the DSSAT model. Five levels of
amendments (0–5–10–20–30 g biochar per kg1 soil) were used and the soil columns remained in the
field for about 30 months until undisturbed soil conditions were reached. No significant differences of the
Kfs values were detected between amended and unamended soils and the ratio between Kfs values was,
on average, equal to a factor of 1.01–0.93–0.98–1.25 (respectively for C5–C10–C20–C30). In the same way,
biochar did not affect appreciably the K(h) values. Depending on the applied pressure head or the biochar
concentration, the differences were within a factor of 0.83–0.39. On the contrary, significant increases of
soil water retention were detected close to water saturation (0 < h <
10 cm) for the highest biochar
concentration. This behavior resulted in an imbalance between the liquid and gaseous phases of the soil.
The relative
field capacity, that gives an account of the optimal balance between water capacity and air
capacity of the soil, was lower than the critical limit of 0.6, suggesting excessive soil aeration. Since these
results are coupled to non-significant differences in rb values, our results confirm that small decreases in
bulk density (on average, 0.014 g cm3) may result in appreciable modifications in soil water retention
close to water saturation. The simulations carried out with DSSAT suggested that a moderate addition of
biochar to a clay soil (not higher than 10 g kg1) has the potential to increase the production of durum
wheat (mean increase
standard deviation, 236
126 kg ha1). These
findings will have to be verified
under
field conditions.