Soil erosion is one of the most important threats to soil quantity and quality, and its unintended consequences can be considered one of the biggest problems facing various ecosystems today. The results of studies in Iran also indicate a high rate of soil erosion. Measurements and estimates show that the amount of water erosion in Iran is between one and four billion tons per year. Therefore, applying appropriate management methods to control soil erosion is of great importance in the management and conservation of natural resources. Since biological control and management of soil erosion and the use of native or non-native vegetation cover are very difficult or impossible in critical conditions and areas prone to erosion, among the various management measures available, it is necessary to use methods that can protect the soil in its place and in the first steps of the impact of erosive factors. One of the most important factors controlling runoff and soil erosion is the use of soil amendments. Therefore, the present study was conducted with the aim of investigating the separate and combined effects of compost, polyacrylamide, and polyvinyl acetate on some chemical, physical, and biological properties of soil, as well as changes in runoff and sedimentation of loess deposits in a rain and soil erosion simulator laboratory.

The soil used in this research was collected from the surface layer (zero to 10 cm) of the loess soil of the pasture lands of Ghozghan Valley, Daregaz city which is sensitive to erosion. After being transferred to the laboratory, to maintain the relative stability of the soil grains, they were passed through a 4 mm sieve. Plots with width, length and height of one, two and 0.25 meters were used for this research. The desired slope of 9% was used, which is roughly proportional to the general conditions of the region. Then, to create an impermeable layer, the plots were filled with mineral pumice to a depth of 15 cm. In order to carry out the present research, compost treatment was used as an organic soil amendments, and polyacrylamide and polyvinyl acetate were used as inorganic soil amendments. Protective treatments were applied in laboratory conditions using a rain simulator with a rainfall intensity of 84 mm/h and with a duration of half an hour and plots of 1*2 m with a slope of 9%. In the review of sources from the researches, anionic polyacrylamide is used in the amount of six grams per square meter and in powder form due to its effect in reducing runoff and sediment, as well as polyvinyl acetate in the amount of six grams per square meter. Compost was used in the amount of 30 grams per square meter. 

Results and Discussion

The use of protective treatments prevented runoff from flowing on the surface of loess soil, resulting in an increase in runoff initiation time and a decrease in runoff and sediment volume. The highest reduction in runoff volume was observed in the combined compost and polyacrylamide treatment at 48%. The highest and lowest sediment concentrations were observed in the two control treatments and the compost  polyvinyl acetate combination, respectively, with values of 267 and 48.5 g/l. The results of the study treatments showed that the use of organic and inorganic compounds also had an effect on the biological properties measured, and these effects were both decreasing and increasing. The use of organic treatments such as compost had a positive effect on the biological properties of the soil due to its high organic matter content and it increases the activity of microorganisms and consequently increases parameters such as microbial biomass carbon, the largest increase being in the combined treatment of polyvinyl acetate and compost at 32%. The combination of compost can lead to improvement of the physicochemical and microbiological properties of the soil. The loss of three nutrients, nitrogen, phosphorus, and potassium, increased, especially in organic treatments compared to the control. Based on the results of this study, the best treatment was the simultaneous use of polyvinyl acetate and compost.

Conclusion

The results of the treatments studied in this study showed that in general, applying organic and inorganic amendments separately and simultaneously reduced the amount of sediment. In general, regarding the effect of the treatments used in this study on the amount of soil loss, it can be said that modifying the physical and even chemical properties of the soil increases its resistance to erosion and erosive agents. Regarding the importance of physical and chemical properties of soil, it can be said that physical properties are more important and their modification is more important in reducing erosion; however, changing and modifying the chemical properties of soil by using various organic additives can also play a role in reducing erosion by affecting physical properties. Each of the organic and inorganic amendments studied was able to affect and change most of the measured parameters, while the simultaneous use of these compounds improved the effectiveness of these compounds in most cases. In summary, it can be stated that the use of compost, polyvinyl acetate, and anionic polyacrylamide, individually and in combination, with the aim of investigating their effects on soil and water conservation and soil chemical and physical properties, can be a useful, efficient, and effective solution. Finally, since the results of these experiments on a laboratory scale show good results, it can be suggested to carry out these treatments on a wider and farm scale.