The Effect of Time and Wetting-Drying Cycles on Durability of Mulches in Soil to Control Wind Erosion

 Wind erosion is one of the important processes of soil degradation in arid and semi-arid regions. Increased soil surface resistance is a key factor to prevent wind erosion. Mulch can increase the resistance of soil surface against erosive agents by creating a coating on the soil surface. The effectiveness of mulch on wind erosion control is on the quantity, type, and durability of the used in dust sources of Iran for stabilizing soil surface against wind erosion. In recent decades, petroleum mulch has been broadly used for stabilizing soil surface against wind erosion in dust sources of Iran. Bio-polymers (e.g. cellulose hydrogel and biochar) and naturally accessible materials (e.g. nanoclay) as environment-friendly mulches can be an alternative to chemical polymers and petroleum mulches. In arid and semi-arid regions, wetting-drying cycles play a crucial role in soil aggregate formation and strength. However, there have been limited studies assessing the impact of wetting-drying cycles on the durability of applied mulches. The main objective of this study was to assess the effectiveness of different types of mulches, including inorganic montmorillonite nanoclay, chemical polyvinyl acetate polymer, and biological biochar and cellulose hydrogel, at various time intervals. The study aimed to improve the physical and mechanical properties of soil, as well as control wind erosion in a loamy sand soil using a wind tunnel. Additionally, the durability of these mulches was evaluated over time after subjecting them to four wetting-drying cycles.

 A factorial experiment was conducted based on completely randomized design with three replications. The factors including mulch type (four levels: nanoclay montmorillonite, polyvinyl acetate polymer, biochar and cellulose hydrogel), mulch concentration (Nanoclay montmorillonite: 0, 16 and 32, Polyvinyl Acetate polymer: 0, 8, and 16, biochar and cellulose hydrogel: 0, 65 and 200 g/m2) and duration (21, 42, 63 and 126 days). The soil used in the wind tunnel experiments was collected from a dust source in the southeast of Ahvaz (Site Number 4). Trays measuring 50×30×5 cm were filled with this soil. The soil surface was then uniformly sprayed with an emulsion of Nanoclay and Polyvinyl Acetate. Additionally, biochar and cellulose hydrogel were mixed uniformly with the soil. Water was sprayed on the soil surface to maintain a constant moisture content of 75% of field capacity. After a specified period, soil properties such as mean weight diameter of aggregates, fractal dimension, penetration resistance, and shear strength were measured. The trays were then placed in a wind tunnel, and a wind erosion test was conducted at a wind speed of 20 m/s for a duration of 5 minutes. The amount of soil loss was measured using the weight method. Then, at each time, the best treatment from each mulch (in terms of reducing wind erosion) was selected and subjected to wet and dry cycles (four cycles).

 The results showed a significant interaction effects (p<0.01) of mulch type, mulch concentration and time factors on soil aggregate stability and fractal dimension, penetration resistance, shear strength were significant (p<0.01). Soil loss decreased in soils amended with biochar and cellulose hydrogel and increased in the case of montmorillonite and polyvinyl acetate polymer over the time. The amount of soil loss in soil amended with cellulose hydrogel decreased by 99.3%. The highest amount of soil penetration resistance and shear strength was observed in cellulose hydrogel mulch at the fourth time which were equal to 1038 and 123 kPa, respectively. Over time, the mean weight diameter of aggregates increased in the soil treated with cellulose and biochar hydrogels, but decreased in the polyvinyl acetate and montmorillonite nanoclay treatments. There was a negative correlation between aggregate stability and the fractal dimension of aggregates. In terms of soil loss, at the fourth measurement time, soils modified with cellulose hydrogels, biochar, polyvinyl acetate, and montmorillonite nanoclay experienced reductions of 99%, 71%, 84%, and 85% respectively, compared to the control. After four wet and dry cycles, the soil loss further decreased by 98%, 64%, 76%, and 81% in the respective treatments, compared to the control.

 In general, it can be concluded that cellulose hydrogel presented the greatest effect on reducing soil loss and controlling wind erosion. In the soils amended with biochar and cellulose hydrogel, the effect of mulches on reducing soil loss increased over the time. However, the opposite results were found in the case of polyvinyl acetate and montmorillonite nanoclay polymers. Therefore, biochar and cellulose hydrogel in the long term and polyvinyl acetate polymer and montmorillonite nanoclay in the short term can control wind erosion. Wet and dry cycles at all durations increased soil loss. But their effect remained on soil loss reduction until the end of the fourth cycle. The results revealed that environmentally friendly biopolymers synthesized from biomass components can be considered as sustainable sources to reduce wind erosion. Bio-polymers are a new window into the use of sustainable biomaterials instead of synthetics in wind erosion control.