Assessment of a Large Subsurface Controlled Drainage and Irrigation System: III. Micronutrient Concentrations in Tile-Drain Effluents.

Controlled subsurface drainage irrigation systems promote crop productivity; however, these land-management systems also afford an efficient pathway for the transport of elements from soils to surface-water resources. Limited research as focused on the chemical composition of tile-drain effluent waters, especially alkali metals, alkaline earth metals, transition metals, metalloids and the rare earth elements. In this manuscript we describe the chemical composition of tile-drain effluents from a 40 ha controlled subsurface drainage-irrigation system and compare the effluent elemental composition with the elemental recoveries from the soil resources using selective extractions. Aqua regia digestion and a water leach extractions shows that Ca, Mg, K, Na and Cl are the dominant macro-elements, whereas other alkali metals, alkaline earth metals, transition metals, metalloids and the rare earth elements are present in secondary to trace abundances. In the tile-drain effluent waters the dominant macro-elements include Ca, Mg, K, Na and Cl, whereas other elements are largely not detectable at traditional detection limits established for inductively-coupled plasma-emission mass spectroscopy (ICP-MS). We conclude that the transport of secondary and microelements in tile-drain effluent waters is very limited because of the complex soil chemistry.      

Key words: tile-drain waters, alkali metals, alkaline earth metals, transition metals, metalloids, rare earth elements.