Soil resistance improvement against windy erosion by bacterium inoculation and addition of some modifiers

Introduction

To enhance soil mechanical properties, eco-friendly materials are needed. Khuzestan Province in the southwest of Iran faces active dust hotspots, highlighting the importance of wind erosion control. In the present study, plant growth-promoting bacteria and biopolymers were used to protect soil against wind erosion. Biopolymers are environmentally friendly materials that are widely used in different geoenvironmental applications. In this research the feasibility of using chitosan and chitosan and lignosulfonate biopolymers for sandy and silt-loam soil stabilization have been studied. Chitosan, a positively charged biopolymer, interacts with soil through various processes like adsorption, forming polymer films, and connecting soil particles. However, despite its advantages, chitosan has not been widely adopted for soil stabilization, erosion control, and dust suppression compared to other biopolymers. Lignosulfonate is an environmentally friendly byproduct from the wood and paper industries, known for its effectiveness in enhancing cohesive expansive soils without major chemical alterations. It is a crosslinked lignin-based polymer with a negative charge that forms metal ion coordination bonds, which compact the soil.



Materials and Methods

Soil with sandy texture was prepared from the surface layer of critical wind erosion areas in southeast of Ahvaz with geographical coordinates of 48°59'N and 31°12'E, and silty-loam texture was prepared from geographical coordinates of 48°51'N and 31°4'E. The experiment was carried out in a completely randomized design in each type of soil. The treatments included control (no treatment), bacterial inoculation (Enterobacter cloacae), calcium lignosulfonate (2% w/v), chitosan (2% w/v), calcium lignosulfonate + bacteria and chitosan + bacteria. A certain amount of soil (7-8 kg) was poured into metal containers with dimensions of 50 × 30 × 3 cm. The bacterial suspension was sprayed separately on soil (1.5 × 106 CFU/ml). Chitosan dissolved at a concentration of 3% by weight in citric acid and lignosulfonate in water were sprayed onto the soil surface. The samples were stored for 60 days. To investigate the effect of treatments on soil wind erosion, a wind tunnel were used. At the end of the experiment, the trays containing the soil samples were weighed using a digital scale and the amount of weight loss of the trays compared to the initial weight was considered as the total amount of soil loss. The penetration and impact resistance of soil were measured. The stability of the aggregates was determined manually by the dry sieving test. The erosion-susceptible particles (EF) and the weighted average diameter of the aggregates (MWD) were calculated.

Results and Discussion

The results of the analysis of variance of the data in silty-loam and sandy soil showed a significant effect of the treatments on the measured characteristics. Comparison of the means with Tukey's test showed that there was a significant difference between the treatments in terms of penetration and impact resistance, MWD and EF in both types of soil at the 5% level. The penetration resistance in loamy-silty soil, in the treatment of chitosan with bacteria, was 3.8 fold, followed by lignosulfonate with bacteria, which was 3.47 fold compared to the control. This increase in penetration resistance in both types of soil was 2.85 fold compared to the control. Impact resistance in the treatments of chitosan with bacteria and lignosulfonate with bacteria in loamy-silty soil decreased by 92% and 72%, respectively, and in sandy soil by 61% and 67% compared to the control. The weighted mean diameter of soil aggregates in the chitosan-bacteria and lignosulfonate-bacteria treatments in loamy-silty soil increased by 2.7 and 2.6 times, respectively, and in sandy soil by 3.6 and 3.4 times compared to the control. The EF decreased with the treatments. In silty-loam soil, chitosan plus bacteria and lignosulfonate plus bacteria treatments had the lowest values with values of 53.1 and 54.8 percent, and in sandy soil with values of 62.9 and 63.05 percent. The comparison test of means showed that the amount of soil loss in silty-loam soil reached zero in chitosan plus bacteria and lignosulfonate plus bacteria treatments. In chitosan, lignosulfonate and bacteria treatments, it decreased by 82, 80, and 69 percent, respectively, compared to the control. In sandy soil, the soil loss in the treatments of chitosan with bacteria, lignosulfonate with bacteria, chitosan, lignosulfonate and bacteria was 87, 86, 74, 73, 53 percent lower than the control treatment. There was a positive correlation between MWD and the penetration resistance and a negative correlation with the impact resistance, EF, and soil loss in both types of soil. Microbial biomass carbon increased with the application of treatments, with the highest amounts measured in the treatment of chitosan plus bacteria, being 2.7 and 2.9 times higher than the control in loam-silty and sandy soils, respectively.

Conclusion

The findings implied that the inoculation of E. cloacae and the application of chitosan and calcium lignosulfonate, compared to the control, increased penetration resistance and MWD. Meanwhile, these treatments reduced EF and soil loss. Among the treatments, the combination of chitosan or calcium lignosulfonate with bacteria was more effective than the individual application of each. Using soil microorganisms, lignosulfonate, or chitosan to improve soil resistance against wind erosion is an environmentally friendly method. Microorganisms and lignosulfonate, in particular, can be easily applied using spraying equipment. However, more field studies are recommended to enable their use on a larger scale. Additionally, the effects of different concentrations of these compounds, as well as their influence on plant-soil interactions and rhizosphere microorganisms, should be investigated.