Soil carbon storage is affected by particle-size fractions and Fe oxides. We assessed soil carbon concentrations in different particle-size fractions, determined the soil chemical composition of the soil, and weathering and mineralogy of sandy soils of the Wisconsin Central Sands, USA. Three land uses were studied (agriculture, forest, and prairie). The soils contained a minimum of 830 g sand kg −1 up to 190 cm soil depth. Approximately 46% of the sand was in the 250-500 µm fraction, and 5% was <125 µm. Soil carbon ranged from 5 to 13 g kg −1 in the topsoil, and decreased with depth. The <45 µm fraction tended to have high concentrations of carbon, ranging from 19 to 43 g kg −1 in the topsoil. Silicon content was over 191 g Si kg −1 , and was lowest in the Bt horizons (191-224 g Si kg −1 ). Up to 29 g Fe kg −1 and 39 g Al kg −1 were present in the soil, and were highest in the Bt horizons. These soils were mostly quartz, and diopside was found throughout the soil profiles.Weathering indices, such as the Ruxton Ratio, showed that the C horizons were the least weathered and the Bt horizons were more weathered. We conclude that most of the carbon in these soils is held in the <45 µm fraction, and soil carbon and total Fe were lowest in the coarser size fractions.2 of 22 capacity [16,[18][19][20]. Because of this, sandy soils under agriculture often need irrigation and fertilizer to produce high crop yields [18,21].The Central Sand Plains covers approximately 6% (8900 km 2 ) of Wisconsin, USA. Much of the soils are intensely cultivated and commonly irrigated, limed, and fertilized. The chemical, physical, and biological components of the soil have changed under agriculture [22]. The carbon stocks are on average 41 Mg carbon ha −1 in the top 30 cm, and this is due to decades nitrogen fertilization and irrigation [23]. The soils under agriculture generally have thicker topsoils (28 cm) than soils under grassland (21 cm) and forest (14 cm) [22]. Madison and Lee [24] determined that quartz was the dominant mineral in the sandy soils of Wisconsin (60 to 96%), and feldspars (orthoclase, plagioclase) were the second most dominant mineral (2 to 12%). The percentage of heavy minerals was low (<3%), and they were primarily opaques (magnetite, hematite, ilmenite, leucoxcene), augite, hornblende, garnet, zircon, and tourmaline [24].The main research question that will be addressed in this paper is: how is carbon stored in sandy soils? The overall objective of this research is to gain a better understanding of carbon storage, elemental composition, and mineralogy of sandy soils. The objective of the research was to: (i) assess soil carbon concentrations in different particle-size fractions, (ii) determine the soil elemental composition in the bulk and particle-size fractions, and (iii) assess the mineralogy and degree of weathering of these soils.