Sustainable crop production on coarse sandy soils is constrained by restricted root growth and poor water and
nutrient retention. Amending with biochar can in some cases increase root depth and improve crop water supply but the mechanisms are not known in details. We added two low temperature, fine-grained gasification biochars (LTST and LTSN) and one fast pyrolysis biochar (FPST) to such soil at concentrations in the interval
0-4wt% and investigated after thorough mixing in the lab their effects on the water retention curve and on soil compressibility. All the biochars increased water contents at equilibrium tension levels known to represent field
capacity (FC) and wilting point (WP). Available water capacity (θAWC=θFC-θWP) increased linearly over the whole range of concentrations. The effect of LTST and LTSN on AWC (on average 3.6 vol% per wt% biochar) was about 70% larger than the effect of the somewhat coarser FPST (2.1 vol% per wt% biochar). The compression index increased on average 21.2 kg m-3 per wt% of biochar regardless of type, showing that the soil became easier to compress with added biochar. Our results indicate that there is considerable potential for better
resource utilization and protection in crop production on coarse sandy soil by ameliorating the subsoil with finegrained gasification biochar or bioash from straw and other biomass.