Soil and Substrata Salinity Trends at Irrigated Glacial Till Sites
There is concern among soil and salinity experts as well as growers that salinity may be building up deep in the soil profile and in substrata at irrigated glacial till sites. This research will determine soil salinity trends at previously sampled benchmark sites as well as a number of new sites and will determine if soil salinity is building up in active root zones and/or substrata to a depth of 6 meters and will attempt to answer the question:
* Is soil salinity building up in soils and substrata on irrigated lands underlain by glacial till parent materials?
The answer to this question will help Reclamation decide if new irrigation developments on glacial till lands are an environmentally and economically feasible way to use available water supplies.
Need and Benefit
Over the years, Reclamation has studied the suitability of glacial till for irrigation development; however, no large projects on glacial landscapes have been approved for construction due in large part to uncertainty about the drainability and irrigability of glacial till lands. Traditional Reclamation testing procedures and drain spacing evaluation techniques predict close drain spacings and high drainage costs.
When the Pick Sloan Missouri Basin Project was completed, it was generally understood that large irrigation projects would be developed by Reclamation in both North and South Dakota. Although intensive studies have been conducted on millions of acres, to date very few glacial lands have been developed by Reclamation for irrigation. In at least two cases. large pumping plants and canals have been built to serve irrigation projects that have not been completed. This has been a source of frustration for many people in the Dakotas since construction of the Pick Sloan Project water storage facilities made large amount of irrigation water available for irrigation development.
Meanwhile many private irrigators have been successfully irrigating their Glacial Till lands with well water and the Canadians have continuously irrigated hundreds of thousands of acres of glacial till lands. Recent improvements in water application technology such as Low Energy Precision Application (LEPA) center pivot systems permit much better water control than was possible in past decades. This will reduce deep percolation incidental to irrigation and should reduce the needs and costs of artificial drainage systems. Many private irrigators currently report high yields, using relatively small amounts of irrigation water and no drainage problems. Reclamation studies conducted in 1999 generally found that active root zone salinity levels in irrigated glacial till soils were at levels that would not reduce yields of the crops commonly grown in the area.
Current thinking among some Canadian and US experts (Barari 1985, Henly 1988, and Jewell 1988) is that dense unweathered glacial till substrata is a barrier to percolating waters and that lateral permeability in glacial till substrata is generally too slow to permit a favorable long term salt balance on lands with little topographic relief that lack deeply incised natural drainage channels. These experts contend that in many areas salts must be building up in subsoil and substrata.
The purpose of this research is to determine if soil and substrata salinity buildup is actually occurring on glacial till lands.
If the findings of this research indicate that no evidence of substrata salinity buildup is occurring then Reclamation would need to reevaluate its policies concerning irrigation of glacial till lands. If the findings of this research indicate evidence of salinity buildup in glacial till substrata, then Reclamation's current approach to glacial till evaluations of irrigation suitability of glacial till lands would be validated.
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