Droughts associated with low or erratic rainfall distribution can cause detrimental crop moisture stress. This problem is exacerbated in the USA’s arid western and southeastern Coastal Plain due to poor rainfall distribution, poor soil water storage, or poorly-aggregated, subsurface hard layers that limit root penetration. We hypothesized that soil physical deficiencies may be improved by biochar applications. Research indicates a single biochar will not serve as a universal supplement to all soils; consequently, biochars may need to be designed with physico-chemical properties that can ameliorate specific soil physical deficiencies. We conducted a laboratory study that examined the effect of biochar on soil moisture retention and aggregate formation. Eight biochars were made from four feedstocks at two different pyrolysis temperature classes (500°C; 932°C) and were characterized for their physical and chemical properties. In addition, we included a biochar made using fast pyrolysis of hardwood wastes. All biochars were mixed at 2% w/w with either a Norfolk loamy sand (Fine-loamy, kaolinitic, thermic Typic Kandiudults), a Declo silt loam (Coarse-loamy, mixed, superactive, mesic xeric Haplocalcids), or a Warden silt loam (Coarse-silty, mixed, superactive, mesic xeric Haplocambids). Amended soils were laboratory incubated in pots for up to 127 days. About every 30 days, bulk density was measured and then each pot was leached with 1.2 to 1.3 pore volumes of deionized water. Gravimetric and volumetric soil moisture contents were determined after free drainage had ceased and again 2 and 6 days after leaching. The Norfolk-treated soils were later dry-sieved, and the sum by weight of their 0.5- to 1.0-mm aggregates was determined. In general, the biochar surface area and surface tension increased when produced under higher pyrolytic temperatures (>500°C). After leaching, Norfolk soils treated with switchgrass biochars had the most significant increase in soil moisture capacities. Similar increases were found in the Declo and Warden soils. Formation of 0.5- to 1.0-mm aggregates in the Norfolk loamy sand varied with biochar. Biochars enhanced the moisture storage capacity of the Ultisol and Aridisols thereby potentially reducing the on-set of crop moisture stress; however, the effect varied considerably with biochar feedstock and pyrolysis temperature
