Saturday, 15 July 2006

Assessing Potential Changes in Soil Salinity from Irrigation Using Electrical Resistivity Technology.

Mike Sharp, David Hopkins, Dean Steele, and Ramesh Gautam. North Dakota State Univ, NDSU- 225 Walster Hall, Fargo, ND 58105-5638

The use of irrigation to alleviate flooding within the Devils Lake Basin has potential implications for the areal distribution of salts. As water is applied in excess of edaphic consumption, soluble salts may mobilize and translocate within the soil profile or landscape. Salts of primary concern include sulfates (SO42-), chlorides (Cl-), and bicarbonates (HCO3-). Spatial and temporal assessment of changes in salinity is critical in evaluating the sustainability of irrigation as a potential solution to the flooding problem. Traditional methods of salinity assessment, such as soil sampling, have proven to be time consuming and labor intensive. The implementation of electrical resistivity technology, such as that of the Veris 3100 Sensor Cart, offers a fast and convenient means of assessing field-scale salinity. The Sensor Cart functions by inducing an electrical current into the soil and collecting georeferenced conductivity data at one second intervals. A Geographic Information System (GIS) is then used to analyze the data and overlay it with other data layers, which may include SSURGO data, digital elevation models, and yield maps. This study is being conducted at 10 northeastern North Dakota sites, eight of which have full-size center pivot irrigation systems; two sites have smaller irrigation systems for specialty crop production. Comprehensive soil investigations, baseline soil sampling, and water balance instrumentation installation was completed by autumn of 2005. Initial calibration of the 66 samples taken during the VERIS surveys show a range in soil Electrical Conductivity (EC) from saturation extracts of 0.29 to 18.9 dS/m. The regression of VERIS sensor reading versus actual soil EC is quite good (r2=0.85), for these spatially variable glacial till soils, and suggests that this technique may be able to discriminate potential changes in soil salinity that may arise from irrigation.

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