Effects of agricultural practices on the hydrodynamics of a deep tilled hardened volcanic ash-soil (Cangahua) in Ecuador

The rehabilitation of indurate pyroclastic formations of the Ecuadorian Sierra (cangahua) paves the way for the development of new agricultural areas. The material derived from the fragmentation of the hardened volcanic ashes is strongly prone to pluvial erosion, essentially because it has a fine silty-sandy texture, and because contains no organic matter and no clay minerals. Rainfall simulation was implemented before and after three cycles of cultivation to asses the evolution of soil structure and its susceptibility to erosion. The cultivated plots were < 1% slope and the rainfall simulation tests were conducted after the harvest on bare surfaces. Two soil preparations, (coarse and fine) and four different agricultural practices, (organic matter, green manure, mineral fertilization, and zero fertilization) were evaluated; as well reference/control plots (uncultivated bare plots). Surface soil crusting occurred rapidly within the cultivated plots when compared to the recent tilled cangahua. Runoff and soil loss were generally higher on plots with lower structural stability and generally exhibited higher clay content. In agreement with the structural stability measured in a laboratory, organic matter inputs increase the soil porosity. This condition had no effect on the structural stability of the soil, resistance to crusting, and therefore little impact on surface runoff and erosion. The preferred option for land with these soils would be no tillage and a permanent soil cover (pasture) if they were to be utilised for agriculture. (c) 2007 Elsevier B.V. All rights reserved.