Irrigation water quality, soil amendment, and crop effects on sodium leaching

Due to prolonged irrigation with water of marginal quality, salination of i rrigated soils in some areas of southeastern Montana has led to a need for better understanding of the soil and water management alternatives for irri gators. A study was conducted with Haverson silty clay (fine-loamy,, mixed, calcareous, mesic Ustic Torrifluvent) to determine the effect of combinati ons of chemical amendments, crop species, and irrigation water quality on N a+ and salt leaching from salt-affected soils. Amendments included CaSO4, P -CaSO4 and MgCl2; also included was a nonamended control treatment. Crops i ncluded alfalfa (Medicago sativa L.), barley (Hordeum vulgare L.), sorghum- sudangrass [(Sorghum vulgare x Sorghum drumondii) (sordan)], and a noncropp ed control. All soil columns (0.15 m x 0.5 m) were irrigated with either hi gh 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 hig h SAR-high TDS water increased the soil solution EC to approximately, 5.5 d S m(-1), but did not decrease crop yields relative to irrigation water havi ng SAR(adj) and TDS of 0.37 and 747 mg kg(-1), respectively. Magnesium disp laced Na+ on the exchange complex, but the effects were short-term compared to CaSO4 Or P-CaSO4. Amendments increased Yields of barley from 14%-27% an d 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 c olumns accumulated the least net soluble salt and Na+. Results of this stud y demonstrate that specific crop and amendment combinations can significant ly affect the efficiency of saline soil reclamation strategies and impact q uality of irrigation return flow.