Effects of Commercial and Paenibacillus tarimensis Exopolysaccharides on Soil Aggregation and Hydraulic Properties of a Saline Clay Loam Soil.

Soil structure and its stability are crucial for water flux and retention, as well as for plant growth and the control of soil erosion, especially in arid regions. Microbial exopolysaccharides (EPS) play a key role in soil aggregation due to their rheological properties, particularly their viscosity, elasticity, and polyelectrolyte nature. EPS-R1 was obtained from Paenibacillus tarimensis REG 0201M, which was isolated from Reggane (Adrar Province, Algeria). The EPS was evaluated for its effects on the physical properties of a calcareous, silty-clay, saline soil, including soil aggregate formation, its stability, and the soil permeability. The bacterial EPS-R1 was produced on Yeast Extract Sucrose Agar, and then both bacterial cells and EPS were recovered and mixed with the soil at three concentrations: 0.2, 0.4, and 0.6% (w/w). Commercial plant and microbial biopolymers viz., gum Arabic and agar-agar, and xanthan gum, respectively, were used to compare their effects. EPS-R1 enhanced macroaggregation markedly at concentrations as low as 0.2%, achieving up to 86.89% of macroaggregates greater than 2 mm at 0.6%. Aggregate stability also improved, with only 12.8% disintegration at 0.6% EPS-R1, when compared with 29.8% with XG. The mean weight diameter showed that treatment with EPS-R1 transformed the soil from a very unstable to a highly stable structure. Furthermore, soil permeability increased by 251% at 0.6%. The water loss kinetics indicated that soil water retention forces decreased with the addition of 0.2% EPS-R1, thereby improving soil aggregate stability. The findings highlighted the potential of EPS-R1 as an effective bio-structuring soil amendment for arid and degraded salt-affected soils.