Investigation of the effect of amount and size of gypsum particles on its performance in the improvement of saline and sodium soils

Extended abstract 1- Introduction Gypsum, sulfuric acid, and sulfur are used to improve saline and sodic soils. In some cases, animal manures are also used, which varies according to environmental conditions and soil type (Jesus et al., 2019). Industrial gypsum is often used to modify saline and sodic soils due to electrolyte maintenance, physical and hydraulic properties (Keren, 1996), low cost, solubility, and ease of use (Amezketa et al., 2005). Gypsum particle size can also affect gypsum performance. Abdolfattah et al. (2015), using gypsum in three different sizes (<0.5, 1-1.5, and 1-2 mm), found that the use of gypsum with smaller particle size has better performance than large particles. Gypsum can reduce salinity as well as soil sodium. Morete and Hiro (2015) showed that the content of soil gypsum has a significant effect on water retention, as the higher the gypsum content, the holding curve soil water holdings have a steeper range and the soil stores more water. In leaching operations and improvement of saline and sodic soils, a large amount of water is required. Therefore, determining the amount of water required due to the water shortage crisis and the protection of water resources is of particular importance. Therefore, in this study, the effect of gypsum modifiers with different amounts and sizes of particles on the amount of water required for leaching saline and sodic soils with low to medium salinity has been investigated. In general, the main objectives of this research are 1- Determining the optimal size of gypsum particles for leaching with minimum water, 2- Determining the optimal amount of gypsum for leaching with minimum water 3- Determining minimum water required for leaching saline and sodium soils. 2- Methodology After drying, the lumps in the soil samples were pounded using a plastic hammer and a unique rolling pin available in the laboratory to prepare the soil. Finally, the compacted soil sample was passed through a 2 mm sieve. Then, using different amounts of sodium chloride, it was transformed into the soil with low to medium salinity and sodium by trial and error in a laboratory. After applying the treatments mentioned in the text of the article to determine the chemical properties of the soil before washing, five different amounts of gypsum (5, 7.5, 10, 25, 50 g of gypsum per kg of soil) were added to the soil in three repetitions and poured into cylindrical pillars. In the preparation of laboratory columns, polyethylene cylindrical containers with a diameter of 35 and a height of 40 cm were used. To drain the laboratory columns in the bottom of the cylindrical containers, a sand filter with a height of 5 cm was used, and pipes for the water outlet were installed in the same part. After 24 hours of treatments and leaching, soil sampling was performed from two different depths (0-15 and 15-30 cm), and soil chemical properties were measured after six leaching steps. The gypsum is passed through different sieves (4, 2, 0.5, 0.25 mm) to obtain different particle sizes in the next step. The treated soils were then tested with three replications as in the previous step, and their chemical properties were measured. After determining the optimal amount and size of gypsum from the last two stages, the soil was leached in six repetitions in 6 stages. After each leaching, one of the treated soils was removed from the leaching cycle and soil and drainage chemical properties. Its output was measured. Finally, soil and drainage characteristics were compared during the repetition of 6 leaching times to determine which stage the leached soil has the desired optimal conditions. Finally, all the mentioned steps were analyzed using SPSS 19 software. 3- Results The results obtained from the application of 10, 25, and 50 g of gypsum per kg of soil showed that if the amount of gypsum used to improve the saline and sodium soils studied is less than 7.5 g of gypsum per kg of soil, the soil retains its salinity and sodium content. If the amount of gypsum used is higher than this amount, the salinity and sodium intensity of the soil will increase. For soil with a depth of 30 cm and a volumetric mass of 1.5 tons per cubic meter, the amount of gypsum required will be about 3.4 tons per hectare. In the continuation of experiments to determine the optimal size of gypsum particles, the tested soil was treated with 7.5 g of gypsum per kg of soil in different particle sizes (0.25, 0.5, 2, and 4 mm). After the significance of the ANOVA test, the average chemical properties of soil in each of the different treatments of gypsum particle size were compared. This finding shows that the optimal gypsum particle size for the study of saline and sodium soils was particle size between 0.25 to 0.5 mm. In the continuation of the research, using the determined optimal amount (7.5 g / kg) and the optimal size of gypsum particle (0.5 mm), the effect of each leaching stage on the soil at two depths (0-15 and 30-15) were examined. According to the results, the lowest amount of ESP is related to saturated flower extract after four washing steps. 4- Discussion & Conclusions This study showed that using 7.5 grams of gypsum per kilogram of soil is the most suitable value for leaching saline and low to medium saline soils (equivalent: 11 tons per hectare to a depth of 10 cm, 16.85 tons per hectare to a depth of 15 cm, and 33.7 tons Per hectare to a depth of 30 cm). The gypsum particle size of 0.5 mm had the best performance in soil remediation. Therefore, it can be stated that adding 7.5 g / kg soil with gypsum particle size (0.5 mm) is the best treatment for soil improvement with low to medium salinity and sodium. This section stated that gypsum treatment with 7.5 g of gypsum per kg of soil and gypsum particle size of 0.5 mm has the best performance after four leaching stages. Finally, in this study, control treatment and gypsum treatment with optimal particle size and size were compared in terms of the effect of different leachates in both surface and deep parts of the soil. Leaching saline and sodium soils without using modifiers causes the soil to become sodic and destroys the soil structure. The results of studies by Noori et al. (2021) have shown that saline and sodium soils that have been partially degraded can be developed for agricultural use by modification with a specific type of treatment and with the best soil management practices.