The cultivated soil; the surface soil as opposed to the subsoil. Xiao et al. (2006) Int. J. Rem. Sensing 27, 12 propose a new index for detecting topsoil grain size composition, and Katra et al. (2007) Geomorph. 86, 3–4 outline dynamics of topsoil moisture. Topsoil erosion occurs when the topsoil layer is blown or washed away; it takes approximately 500 years for one inch of topsoil to be deposited, but there are 25 billion tons of topsoil lost each year. See Lovett et al. in E. Buhmann et al., eds (2006) on modelling and visualizing soil erosion, and Evans (2006) CABReviews 1, 30 for a review of sustainable practices to limit soil erosion.