Quantifying Biochar Impacts on Plant Available Water and Water Use Efficiency.

The inability of soils to hold enough plant available water (PAW) between rainfall events often limits crop productivity. Most studies have shown that biochar amendments decrease soil bulk density and increase soil water retention. However, limited knowledge exists regarding the ability of biochar to influence PAW and water use efficiency (WUE). Furthermore, there is limited knowledge about how biochars age in soil environments and whether changes in their chemical, physical, and biological properties during aging influence PAW and WUE. This greenhouse study using repacked soil columns investigated the influence of biochar and biochar age on PAW and WUE for three contrasting soils. Soil columns (1 kg soil) were watered, fertilized, and planted with three maize seeds per column. At the V1 growth stage, the seedlings were thinned to one plant per column, the soil columns were watered to field capacity, and subsequently no additional water was applied. Relative to the controls, both fresh and aged biochars increased water retention in silty and clay loam soils, but in a sandy soil fresh biochars increased and aged biochars decreased soil moisture retention. Final biomass weight increased in response to the biochar treatments for the silty and sandy soils but decreased for the clay loam soil, suggesting that the increased water held in the clay loam soil was not plant available. Amendment with aged biochars increased biomass production for the silty and clay loam soils relative to fresh biochars with the opposite trend observed for the sandy soil. Results of this experiment indicate that biochar and biochar age impact PAW and WUE, however, the effect is soil and biochar type dependent. This study provides critically needed data for calibration of the new biochar module within the APSIM cropping systems model.