Salt-affected soils of the coastal plains in Rio Grande do Sul, Brazil

In Rio Grande do Sul (RS) State, Brazil, the soils are not prone to salinization due to the large amounts of rainfall, which are sufficient to leach the soluble salts. However, flooded rice crops grown in the coastal plains of RS may be affected by soil salinity, once the soils in this region are formed by marine, fluvial-lacustrine sediments. The use of water for irrigation of crops from sources connected with the Atlantic Ocean, especially Patos Lagoon, can lead to deposition of excessive amounts of sodium in the soil, especially in southern portion, by the proximity to channel linking the lagoon to the sea. This study aimed to map the occurrence of salt-affected soils in the coastal plains of RS State, Brazil. The study was performed in three regions: Internal Coastal Plain (ICP), External Coastal Plain (ECP) to Patos Lagoon and North Shore. 766 georreferenced soil samples were collected and levels of exchangeable sodium, exchangeable sodium percentage (ESP) and electrical conductivity (EC) of saturated extract (ECse) were analyzed. The resulting analytical data of the sampling points were submitted to a descriptive statistic and used to generate maps aiming to depict the continuous spatial variation of each measured variable. Most of soil samples showed indicators of low soil salinity, especially in most of the ICP and North Shore. The soils most affected are concentrated in regions overlapping the paleochannels sub-surface previously identified in the sub-surface of the ECP and in areas closer to links between sources of freshwater and sea. In the ICP, the salinity problem was restricted to only some areas due to the use of saline water from Patos Lagoon.