Biochar Effects on Soybean Root Growth and Plant Water Status.

A better understanding on complex root responses and plant water status when biochar is added to the soil will optimize the use of this soil amendment. Crop responses depend on cropping and tillage systems, and biochar application rate and method (e.g. topdressing vs incorporating). A lysimeter experiment was established under greenhouse conditions to investigate the effects of topdressing or incorporating biochar in the top 0.15 m of the soil profile at three rates (10, 25, and 50 Mg ha-1) in combination with full and partial irrigation strategies on soil water dynamics, soybean (Glycine max L.) shoot biomass accumulation, and root architecture during early vegetative growth. Soil incorporation of 25 and 50 Mg biochar ha-1 increased leaf area by 29% and 31% compared to topdressing 50 Mg biochar ha-1 and to the non-treated control, respectively. Similarly, the incorporation of 25 and 50 Mg biochar ha-1 exhibited 25% higher fresh weight compared to the non-treated control. Topdressed biochar increased soil pH more than incorporated biochar treatments in the upper 0.15 m of the soil profile. Biochar at 10 and 25 Mg ha-1 increased root length density (RLD) and root surface area (RSA) in the 0-0.05 m soil layer. In the 0.05-0.15 m soil layer, only incorporation of 10 Mg ha-1 increased 38% RLD. Similarly, incorporation of 10 and 25 Mg biochar ha-1 increased RSA 43 to 49% compared to the control and all topdressed rates. Incorporation of biochar can increase soybean RLD and RSA favoring more efficient absorption of water and nutrients in the soil. This could be especially beneficial under limiting conditions such as those in areas with poor soils or dry periods.