The Efficiency of Arabic Gum on Improvement of Physical and Chemical Properties of Saline-Sodic and Non-Saline-Sodic Soils near Lake Urmia

The use of soil amendments more specifically bio-polymers is increasing nowadays. Arabic Gum is also one of the hydrogels that are capable for soil modification. It seems that the main usage of amendments in soils is to improve the structure of intended soils. Saline-sodic soils are among the poorly structured soils. The use of soil amendments in these soils may be of the most concern. The different conditions of saline-sodic soils in terms of microbial activity and sodium concentration imply that there should be differences in effects of different soil amendments in saline-alkaline and non-saline-alkaline soils. There is no report (up to our knowledge) about the application of Arabic gum in saline soils. However, it seems that the effects of Arabic gum in saline-sodic soils may differ from what in non-saline-alkaline soils due to the interactions between Arabic gum, salinity, and sodium. Therefore, the current research was aimed to investigate the effects of Arabic gum as an analogue of exopolysaccharides on several soil characteristics of saline-sodic and non-saline-sodic soils collected from Lake Urmia catchment, northwest of Iran.

The current research was carried out using loam soil samples collected from Qareh Chopogh village located on the southeastern border of Lake Urmia, Bonab plain, Northwest of Iran. In order to evaluate the effects of Arabic gum on properties of salin-sodic and non-saline-sodic soils, a factorial experiment based on completely randomized design (CRD) with two factors (salinity - sodicity levels and Arabic gum) and three replications was carried out. Salinity - sodicity levels, as first factor, included  EC = 1 dSm-1 and SAR = 1.3 (non-saline-sodic soil), EC = 6 dSm-1 and SAR = 16 (saline - sodic soil), and EC = 30 dSm-1 and SAR = 58 (severely saline-sodic soil). When soils were sampled from each salinity-sodicity classe and transformed to laboratory, pots were prepared and treated with different levels of Arabic gum including 0, 5, and 10 g kg-1 and incubated for one month with varying soil water content between around 0.5FC and FC. After incubation time, disturbed and undisturbed soil samples were collected from pots and were prepared for further analysis. Undisturbed soil samples were used to determine bulk density of pots (Db), volumetric (θv) and gravimetric (θm) saturated soil water contents, and saturated hydraulic conductivity (Ks). Disturbed soil samples were also used to determine wet-aggregate stability (WAS), mean weight diameter (MWD), and mass fractal dimension (Dm) of soil aggregates, soil pH, soil organic carbon (OC), soil cation exchange capacity (CEC), and soil respiration. Finally, results were subjected to analysis of variance in SAS software based on applied design.

The interaction of Arabic gum and soil salinity-sodicity was significant for organic carbon, microbial activity and soil structural characteristics (MWD, WAS, and mass fractal dimension). Arabic Gum improved biological soil properties even in saline-sodic soils. The higher microbial activity (16 to 443 mg CO2 kg-1 soil day-1 in higher amount of Arabic gum vs. 3 to 109 mg CO2 kg-1 soil day-1 in blank soil) and organic carbon content (0.31 to 0.36 % in higher amount of Arabic gum vs. 0.14 to 0.22 % in blank soil) were obtained in higher amount of Arabic gum in saline-sodic and non-saline soils. While, the stability (0.88 to 60 vs. 0.9 to 13 %), mean weight diameter (0.06 to 2.53 vs. 0.009 to 0.46 mm), and mass fractal dimensions (0.935 to 2.09 vs. 0.75 to 2.45) of soil aggregates were affected by Arabic gum in non-saline-sodic soils rather than saline-sodic soils. The main effect of soil salinity-sodicity was significant for soil cation exchange capacity, soil pH, gravimetric and volumetric soil water contents, and pots bulk density. The higher amounts of CEC (21 vs. 9 Cmole+.kg-1), pH (8.0 vs. 7.4), volumetric (53 vs. 41 %) and gravimetric (43 vs. 30 %) water contents, and the lower pots bulk density (1.23 vs. 1.37 g.cm-3) were recorded in severely saline-sodic soil compared to non-saline-sodic soil. The main effect of Arabic gum was significant for soil saturated hydraulic conductivity and soil pH where the higher rate of saturated hydraulic conductivity (0.06 cm.min-1 in higher amount of Arabic gum vs. 0.04 cm.min-1 in blank soil) and the lower pH (7.9 in higher amount of Arabic gum vs. 8.2 in blank soil) were recorded in 10 g.kg-1 Arabic gum.

Based on the results, we conclude that although the effectiveness of the Arabic gum is decreased in saline-sodic soils, it significantly affects different soil characteristics. However, it seems that we need to apply higher amount of Arabic gum (higher than 10 g.kg-1) to gain the considerable effects of Arabic gum in saline – sodic soils. Since gradual drying of Urmia Lake, located in northwest of Iran, is leaving behind wide areas of saline and saline-sodic soils which is threatening habitant’s health, modification of these salt-affected areas using Arabic gum can be a useful strategy. Although, improving vegetation density seems to be main key for this aim, application of soil amendments (more specifically Arabic gum) may support the establishment of vegetation in area. Our objective observation also points to this fact that Arabic gum (specifically in higher amount of 10 g.kg-1) resulted in a crust like layer in soil surface specially in dry state that can prevent the removal of salt particles by the wind. However, the effectivity of Arabic gum in preventing the removal of salt particle by the wind (which is a common issue in area) needs to be evaluated through wind tunnel experiments.