Trace and major element associations in basaltic ash soils of El Hierro Island

Associations between major and trace elements (aqua regia) were studied in basaltic-ash soils from the island of El Hierro in order to distinguish possible non-lithological contributions to the large trace element concentration shown by the soils. Soil composition reflected the basaltic composition of the parent materials and their extended tendencies to ultrabasic and trachytic compositions. The obtained values did not differ from previously reported reference values for natural soils, pointing to a low intensity anthropic activity. Only Cd levels were above those predicted by parent materials. The large soil total phosphorus (P) concentrations were consistent with those reported for the parent materials, thus obscuring the hypothesis of the contribution of the phosphate-rich Saharan dust to soil Cd enrichment. The spatial distribution of trace and major elements helped to identify a larger concentration of trace elements in soils of the most humid zones where andic properties were more highly expressed. Anthropic influence was revealed by the association of P and Cd in a former intensive agricultural zone. The large metal concentrations could reach or exceed the Soil Quality Standards for heavy metal concentrations in relation to soil pH. Plant composition, however, did not approach hazardous levels, probably due to the effect of the organic and highly reactive mineral sorbing phases of the studied soil types. © 2014 Elsevier B.V

Subsurface drip irrigation and reclaimed water quality effects on phosphorus and salinity distribution and forage production

In the Canary Islands, water scarcity is one of the constraints for agricultural activity. Non-conventional water resources generally represent more water volume than conventional ones. The distribution of these resources frequently permits the possibility of a conjunctive use of desalinated (DW) water and reclaimed municipal wastewater (RW). Field testing with both water qualities and different irrigation systems is necessary for optimal site-specific management. The objective of this work was to evaluate soil salinity and phosphorus distribution, and alfalfa yield in a 20 month field experiment carried out in the island of Gran Canaria, using municipal RW and freshwater (FW) under subsurface drip irrigation (SDI). Phosphorus speciation was performed both in irrigation waters and in soils (Olsen's inorganic, organic, and microbial). RW had large EC values (2.4dSm-1) with a remarkable nutrient load contribution and an average total P around 3mgL-1, predominantly hydrolysable forms, while FW had very low salinity and negligible amounts of P. For the RW treatment a salt gradient was established, causing plant mortality between the irrigation lines. The study of P speciation allows describing P distribution and plant uptake in terms of P forms. Large values of microbial P were produced for the two irrigation waters around the emitters, especially for FW. A faster P-cycling could have contributed to the significantly larger inorganic P contents observed in FW irrigated soils, in spite no external sources were added by the irrigation water.Subsurface drip irrigation Desalinated water Reclaimed municipal wastewater Water-saving Alfalfa (Medicago sativa)