Quantifying the influence of Eucalyptus bark and corncob biochars on the physical properties of an oxisol under maize cultivation

Studies of the effect of biochar on soil physical and hydric properties report contradictory results; biochar properties, soil type, and agricultural system may all influence these effects. In the present study, we assessed the impact of biochars from slow pyrolysis, about 300◦C, of eucalyptus tree bark and corncobs, applied at the rate of 15 t.ha-1, on physical and hydraulic parameters of an oxisol in Cameroon (texture of clay loam). The biochar was incorporated into the top 15 cm of the soil in a maize production system. The land was cultivated either flat or as furrows and ridges; also, a treatment of buried straw (or not) was employed. Measured physical parameters were carried out in the laboratory on undisturbed soil samples collected from each of the 30 plots (5-10 cm depth), at the end of either 6 months (first production), or 12 months (second production). Soil bulk density was greater in plots on flat land (p = 0.0002) compared to furrows and ridges; it was not affected by type of biochar (p = 0.78). Total porosity remained unchanged by the biochar application, however, it was higher during the first production period compared to the second (p = 0.021). Soil available water content (AWC) was higher in flat plots compared to furrows-ridges plots (p = 0.054) during the first production period, but lower during the second period (p = 0.0004). Flat plots with buried straw had better AWC than furrows-ridges plots; flat plots also had higher residual (p < 0.0001) and saturated (P = 0.0006) water content compared to furrows-ridges plots. In general, we found no evidence that application of biochar improved the physical and hydraulic properties of the oxisol in this particular agricultural system. However, soil cultural treatments did affect the physical properties and water retention of the soil.