This study aimed to investigate the effects of calcium- and/or aluminum-based soil amendments on soil quality and sunflower yield in the Hetao Irrigation District of Inner Mongolia, China, so as to provide a theoretical support and technical guidance for the comprehensive governance of saline-alkali lands in the region.

A two-year (2022-2023) field experiment was conducted in Ordos City, Inner Mongolia, with four treatments: control (CK), calcium-based amendment (Ca-based), aluminum-based amendment (Al-based), and calcium+aluminum-based amendment (Ca+Al-based). The experiment systematically assessed soil salinity indices and nutrient content in the 0-20 cm soil layer, as well as sunflower agronomic traits and grain yield at harvest. The soil quality index (SQI) was constructed using principal component analysis, and structural equation modeling was employed to reveal the effects of the amendments on SQI and sunflower yield.

Compared with CK, all three soil amendments improved the SQI and sunflower yield. Among the treatments, the Ca+Al-based amendment demonstrated the most promising results, specifically reducing soil pH by 0.09-0.24 units and sodium adsorption ratio by 14.3%-24.9%, and increasing soil available phosphorus by 72.7%-147.0% and nitrate nitrogen by 0.6%-89.6%. Consequently, it increased the SQI by 51.0%-58.0% and sunflower seed yield by 30.0%-51.4% compared with CK. The Ca-based treatment was less pronounced, with SQI increasing by 36.3%-51.0% and yield increasing only in 2022 (29.3%). Notably, soil electrical conductivity increased by 16.0%-70.4% under the Ca-based and Ca+Al-based treatments, primarily due to an increase in water-soluble Ca²⁺, Mg²⁺, and SO₄^2- concentrations, and did not lead to salt damage in plants. In addition, structural equation modeling revealed that the amendments exerted their effects by directly regulating soil salinity and nutrient indices, which indirectly increased SQI and yield. Furthermore, the contribution of soil salinity reduction to yield (79.2%) was greater than that of nutrient improvement (20.8%).

The Ca+Al-based amendment demonstrated a synergistic effect in significantly improving soil quality and sunflower yield, making it a suitable option for further application in the Hetao Irrigation District of Inner Mongolia and similar ecological regions.

Saline-alkali soil is an important reserve resource of cultivated land and potential granary in China, and its management and utilization are related to national food security. Therefore, innovative techniques and amendments should be developed to address these challenges in saline-alkali regions. Among these, calcium supplementation is recognized as one of the most effective methods for ameliorating saline-alkali soil. In the past two decades, gypsum from the desulfurization of flue gas (FGDG) in coal-fired power plants has become a preferred calcium source for ameliorating saline-alkali soil because of its high calcium content and economic feasibility. Given that FGDG has developed into a soil amendment and has been widely used, a profound understanding of the progress of its patents can provide technical guidance for the large-scale amelioration of saline-alkali soil.

Based on the incoPat global patent database, a bibliometric analysis was conducted on 520 invention patents in the field of using FGDG to ameliorate saline-alkali soil from 2003 to 2022. The application and authorization trends, high-yield mechanisms, operational status, substance composition, and their correlation with patents in this field were systematically analyzed. In addition, a comparative analysis was conducted on the effectiveness of 52 patents with application cases.

The results showed that the annual number of patent applications for using FGDG amendments to ameliorate saline-alkali soil has a trend of first increasing and then decreasing, with a peak period of 115 patents in 2016. Most patents take 20-30 months from publication to authorization. However, the overall proportion of authorization has shown a decreasing trend. The number of patents granted by universities and research institutes is higher than that granted by enterprises, whereas the number of patents jointly granted by universities and enterprises accounts for 15.6% of the total. A total of 37 patents were converted, 7 of which were pledged, accounting for 33.3% of the total number of grants, all of which were transferred by universities to enterprises and pledged by enterprises for financing. More than 70% of patents comprised three or more substances, primarily including organic and inorganic minerals, microbial agents, and nutrient supplements. Organic materials can directly provide nutrients for the soil to make up for the shortage of FGDG in terms of nutrients, with the frequency of application as high as 95.7%, followed by inorganic minerals, which account for 44.5%; microbial agents, which account for 41.3%; and nutrient supplements, which account for 21.3%. Compared with soils with or without other types of amendments, the application of FGDG amendments significantly decreased soil pH, exchangeable sodium percentage, and salt ions that are toxic to crop growth and increased soil Ca²⁺, SO₄^2-, and total/available nitrogen and phosphorus contents, which provided a better soil environment, thereby increasing crop yield.

Generally, research and development on FGDG amendments for saline-alkali soil amelioration have matured, and some innovative achievements have been transformed into real productivity; thus, the value of related patents has been increasingly highlighted. However, problems such as the relatively simple composition of current patents, unclear technical requirements for the amount of application and method, and serious homogeneity of patents have been encountered. In the future, we should strengthen the cooperation among schools, enterprises, universities, and research institutes, intensify research on the FGDG formula used in saline-alkali soil, and enhance the application benefits of FGDG amendments.