11. Porosity of subsurface soil is lower than in surface soil due to compaction by gravity. 12. Strongly developed Planosols with a very silty or sandy surface soil are best left untouched. 13. Most roots in surface soil are " long ropelike laterals of secondary and tertiary origin ". 14. Some of the contaminated soil has blown off-site and affected nearby surface soil and surface water. 15. It is thought that the fine roots help keep the surface soil together and prevent surface erosion. 16. This iron carbonate then combines with the surface soil and, over time, hardens into a solid mass. 17. The species is able to exploit high levels of nitrogen in surface soil to achieve local dominance. 18. Blocky structures are common in subsoil but also occur in surface soils that have a high clay content. 19. The saw effect took off the surface soil of the island and took down the trees and vegetation. 20. When environmental conditions are just right, the bacteria can " bloom " and re-contaminate surface soil and grass.
