The Influence of Phosphogypsum on the Salt Composition of Salinated Soil

Abstract

Global climate changes in many countries of the world lead to the need to use irrigation as a driving factor for obtaining guaranteed and stable harvests of agricultural crops. Irrigation with water of different quality leads not only to an increase in the yield, but also to a change in the salt composition of the soil. The change in the salt composition of soils occurs much faster during irrigation with mineralized water, which leads to the accumulation of soluble salts in the arable layer of the soil and the deterioration of the composition of the soil absorption complex. Accumulation of sodium ions leads to salinization of irrigated soils. It is possible to stop or suspend the salinization processes by introducing chemical melioration with calcium-containing meliorants. As an ameliorant in this work, the use of a by-product of the mineral fertilizers production – phosphogypsum, which contains a significant amount of calcium (up to 95%), replacing exchangeable sodium in the soil absorption complex is proposed. Our researches are related to the establishment of optimal calculation norms and terms of phosphogypsum application, their influence on the change in the components of the soil’s saline extract. The research was conducted on soils that had been irrigated with mineralized water from the Samara River (Ukraine) for a long time (over 50 years). According to the amount of exchangeable sodium, the soils of the experimental sites belonged to low-sodium soils with physical signs of salinization processes, and according to the content of toxic salts-moderately saline. For phosphogypsum in the soil-ameliorative conditions of the Northern Steppe of Ukraine, the ameliorative, agronomic, and ecologically safe rates of introduction in spring and autumn were calculated. The scheme of experiments provided options with sprinkler irrigation and without irrigation. The composition of the aqueous extract was determined by indicators of anion-cation content. During the research, a gradual decrease in the number of sulfates was observed: by 1.5% in the second year after exposure, and by 7.5% in the third year after exposure to phosphogypsum. The number of hydrocarbons decreased in irrigated areas where phosphogypsum was applied, and an increase in their content was observed in areas where irrigation was not carried out. Irrigation options were characterized by a significant increase in the content of chlorine ions, which is explained by the arrival of these ions exclusively with irrigation water. The degree of salinity was determined by pH and sodium adsorption ratio (SAR). Based on these indicators, it was established that the soils are slightly saline in all variants of the experiments. As a result of multi-year research, a positive effect of phosphogypsum melioration on the anion-cation composition of water extract and the degree of soils salinity irrigated with mineralized water for a long time was noted. According to the anionic composition, the chemistry of the soils in the experimental plots was sulfate in the variants where phosphogypsum was applied and vegetation irrigation was carried out and without irrigation, while in the control plots (without phosphogypsum and without irrigation) soda-sulfate chemistry was characterized. The chemistry of the soils in the experimental areas according to the cationic composition was sodium in all versions of the experiments. According to the sodium-adsorption ratio (SAR), the degree of soil salinization belonged to the slightly saline type, while the average type of salinity remained in the control plots without phosphogypsum.

Agroecological Transformation in the Salt Composition of Soil under the Phosphogypsum Influence on Irrigated Lands in Ukraine

“…The application of phosphogypsum, as in many previous studies [14,60], led to a reduction in the sodium-ion content [22]. In this case, salinisation processes caused by an excessive sodium content in the soil absorption complex are slowed down, resulting in improved physical properties of the soil.…”

“…The practical experience of using phosphogypsum under the conditions of the Steppe zone of Ukraine (Haplic Chernozems) is represented by a small number of scientific publications [14,16,32]. Therefore, we hope that this study can be useful in expanding scientific knowledge and approaches in the fight for the ecological improvement of soil cover in similar climatic zones and conditions of irrigated agriculture.…”

“…It is worth noting that among these 388 thousand hectares (as of 2018), the main negative impacts of irrigation water on soils are as follows: 342 thousand hectares are at risk of waterlogging and 46 thousand hectares are at risk of toxic effects on plants and secondary salinisation. About 13 thousand hectares are irrigated with water of high mineralisation, which is not suitable for irrigation [14]. This requires the implementation of measures to prevent or slow the processes of salinisation and alkalinisation when irrigating with poor-quality water [15,16].…”