Biochar amendment to coarse sandy subsoil improves root growth and increases water retention

Crop yields and yield potentials on Danish coarse sandy soils are strongly limited due to restricted root growth and poor water and nutrient retention. We investigated if biocharamendment to subsoilcan improve root development in barley and significantly increase soil water retention. Spring barley ( Hordeumvulgare cv. Anakin) was grown in soil columns (diameter: 30 cm) prepared with 25 cm topsoil, 75 cm biochar-amended subsoil, and 30 cm un-amended subsoillowermost placed on an impervious surface. Low-temperature gasification straw- biochar(at 0, 0.50, 1.0, 2.0, and 4.0 wt%) and slow pyrolysis hardwood- biochar(at 2 wt%) were investigated. One wt% can be scaled up to 10 2 Mg/ha of char. After full irrigation and drainage, the in-situ moisture content at 30-80 cm depth increased linearly (R2 = 0.99) with straw- biocharcontent at a rate corresponding to 0.029 m 3 /m 3 /%. The lab determined wilting point also increased linearly with char content (R 2 = 0.99) but at a much lower rate (0.003 m 3 /m 3 /%). Biocharat concentrations up to 2% significantly increased the density of roots in the 40-80 cm depth interval. Addition of 1% straw- biocharhad the most positive effect on root penetration resulting in the highest average root density (54% coverage compared to 33% without biochar). This treatment also resulted in the greatest spring barley grain yield increase (22%). Improving the quality of sandy subsoilshas global potentials, and incorporation of the right amount of correctly treated residues from bioenergy technologies such as straw- biocharis a promising option.