Salinity and Sodicity Changes under Irrigated Alfalfa in the Northern Great Plains

Insufficient water is the greatest limitation to crop production and choice of crops grown in the Northern Great Plains. Supplemental irrigation can overcome this limitation. Uncertainties about the drainage capacity of fine-textured subsoils and the effect of irrigation on soil properties have impeded irrigation development. In this study we quantified salinity changes in soils with fine-textured subsoils receiving a range of irrigation treatments. Alfalfa (Medicago saliva L.) was planted in 18 non-weighing lysimeters at two sites having fine-textured subsoils. Irrigation was applied at three levels so that irrigation plus precipitation equaled either one, two, or three times the calculated evapotranspiration rate using two water qualities (electrical conductivity of irrigation water [EC1] 0.1 S m‒1, sodium adsorption ratio of irrigation water [SARi] 4; or ECi 0.34 S m‒1, SARi 16). Changes in the electrical conductivity of saturated soil extracts (ECe) and the sodium adsorption ratio of saturated soil extracts (SARe) were determined from soil cores collected to a depth of 1.5 m nine times between the years of 1984 and 1993. Averaged across irrigation levels, the profile-averaged ECe increased from 0.03 to 0.12 S m‒1 and the SARe increased from 1 to 6 in lysimeters receiving the 0.1 S m‒1 water. In lysimeters receiving the 0.34 S m‒1 water, the profile-averaged ECe increased from 0.03 to 0.23 S m‒1 and the SARe increased from 1 to 11. Salinity exhibited seasonal fluctuations. Changes in sodicity were persistent, exhibiting little seasonal variation. Supplemental irrigation of alfalfa is a viable management option in the Northern Great Plains when irrigation water quality is not a problem