Assessing Leaching of Saline-sodic Soils Affected by Kaveh-Soda Factory Effluent using Georeferenced Maps in Maragheh-Bonab Plain

Abstract

Relativity of soil maps may limit their utility at many aspects such as agriculture development, farming, civil engineering, urban and regional planning and forestry. Paying attention to the scale is one of the most common procedures in assessing the maps usability. The average size delineation (ASD), effective scale number (ESN), index of maximum reduction (IMR) and shape complexity index (SCI) are the maps quality criteria that can be examined. The purposes of this study were: a) to evaluate the EC and SAR maps of the farm lands affected by the Kaveh-Soda factory effluent on the basis of the above quality criteria and b) to evaluate the efficiency of continuous and intermittent methods of leaching in three Saline-Sodic soils with loam and sandy loam textures. EC maps of the area were selected and ASD, ESN, IMR and SCI were determined as 0.95 cm², 1:26000, 1.54 and 3.33, respectively. For the SAR maps the above criteria were 1.33 cm², 1:31000, 1.84 and 3.51, respectively. According to the above criteria there should be no limitation in their uses for developing of agricultural and civil engineering projects. It is known that optimum IMR is equal to 2, so that raising IMR of EC and SAR maps from 1.54 and 1.84 to 2 led their scale to increase from 1:34000 to 1:26000 and 1:31000, respectively and increase maps contrast as well. At the subsequent stage, efficiency of two leaching methods of saline-sodic soils was examined after knowing the usability of the maps and separating their units, as affected by Kaveh-Soda factory (Maragheh). For this purpose, PVC tubes (Lengths= 70 cm; Diameter= 10 cm) were prepared and filled with soil (5200 g sieved by 4.76 mm). The flow rate during both leaching methods was selected to be 1.25 K_S of the columns. Soil columns were grouped according their EC as 1) EC= 10.38 dSm^-1, with Na⁺= 49.64 meqL^-1; 2) EC= 20.6 dSm^-1, with Na⁺= 94.57 meqL^-1; and 3) EC= 36.6 dSm^-1, with Na⁺ = 166.11 meqL^-1. Leaching water was saturated with gypsum because of it's high SAR to disperse the soil and effectively reduce the leaching efficiency. The EC of leaching water was 2.34 dSm^-1. Leaching was stopped when EC of the effluent from the columns became relatively constant. The results revealed that intermittent leaching method efficiency was 8% greater than that of continuous method. The depth water need for the reclamation of the affected soils was also calculated.