A paddy on sodic varved sediment and plant life constraints, NE Spain

Abstract

In arid lands, irrigation is necessary for agriculture to be profitable. However, the nature of soils and parent materials is significant enough to trigger permanent management limitations and the loss of important investments, as happened in some areas of the Flumen irrigation district in the Central Ebro Basin, NE Spain. We studied the distinct soil characteristics of a salt-affected agricultural plot and its recurrent problems from the last 30 years. We describe and discuss the prominent features of this soil and their effects on plant life and agricultural management. The evidence of post-irrigation salt-related effects is documented together with the water and soil salinity monitoring records. The presence of varved Holocene sediments comprising alternating clays and carbonate-rich silt with high levels of salinity and sodicity, together with a shallow saline water table, were found to be the key unfavorable conditions. Despite a noticeable decrease in sodium adsorption ratio (SAR) from 1999 to 2015 and a reduction in soil salinity down to a steady state after rice paddy cultivation, SAR and alkalinity remained high enough to hamper irrigated agriculture. Only the native plant Puccinellia festuciformis thrives in the studied plot. The article presents and discusses chemical features―analytical data―and morphological features―pictures and descriptions―that are seldom reported and interpreted together in the scientific or technical literature about irrigation of sodic soils, often limited to chem data. The paddy field studied is deemed representative of the most unfavorable soils for agriculture in the irrigated districts of the Ebro valley.