Irrigation Water Quality, Soil Amendment, and Crop Effects on Sodium Leaching

Due to prolonged irrigation with water of marginal quality, salination of irrigated soils in some areas of southeastern Montana has led to a need for better understanding of the soil and water management alternatives for irrigators. A study was conducted with Haverson silty clay ( fine-loamy, mixed, calcareous, mesic Ustic Torrifluvent ) to determine the effect of combinations of chemical amendments, crop species, and irrigation water quality on Na + and salt leaching from saltaffected soils. Amendments included CaSO 4 , P-CaSO 4 and MgCl 2 ; also included was a nonamended control treatment. Crops included alfalfa ( Medicago sativa L.) , barley ( Hordeum vulgare L.), sorghum-sudangrass [( Sorghum vulgare 2 Sorghum drumondii ) (sordan)] ,and a noncropped control. All soil columns (0.15 m 2 0.5 m) were irrigated with either high Na + adsorption ratio (SAR adj = 16.6) , high total dissolved solids (TDS = 1647 mg L -1 ) water, or low SAR adj (1.15), low TDS (747 mg L -1 ) water. Drainage volume, electrical conductivity (EC), SAR, Na + of drainage water, and Na + leaching were monitored over three crop cycles. Irrigation with high SAR-high TDS water increased the soil solution EC to approximately 5.5 dS m -1 , but did not decrease crop yields relative to irrigation water having SAR adj and TDS of 0.37 and 747 mg kg -1 , respectively. Magnesium displaced Na + on the exchange complex, but the effects were short-term compared to CaSO 4 or P-CaSO 4 . Amendments increased yields of barley from 14%-27% and alfalfa by 25% but had no effect on sordan. Columns cropped to barley had 28% greater Na + leaching than columns planted to other crops. Noncropped columns accumulated the least net soluble salt and Na + . Results of this study demonstrate that specific crop and amendment combinations can significantly affect the efficiency of saline soil reclamation strategies and impact quality of irrigation return flow.