The systematic removal from the seed production field of off-types, plants of another crop or variety and diseased plants. (Seeds toolkit, FAO, 2016 (http://www.fao.org/3/a-i6397e.pdf).)
Luvisols have a higher clay content in the subsoil than in the topsoil, as a result of pedogenetic processes (especially clay migration) leading to an argic subsoil horizon. Luvisols have high-activity clays throughout the argic horizon and a high base saturation in the 50–100 cm depth. Many Luvisols are known as Texturally-differentiated soils and part of Metamorphic soils (Russia), Sols lessivés (France), Parabraunerden (Germany), Chromosols (Australia) and Luvissolos (Brazil). In the United States of America, they were formerly named Grey-brown podzolic soils and belong now to the Alfisols with high-activity clays. (IUSS Working Group WRB. 2015. World Reference Base for Soil Resources 2014, update 2015 International soil classification system for naming soils and creating legends for soil maps. World Soil Resources Reports No. 106. FAO, Rome.)
