Effects of Lignite Humic Acid and Lignite Humic Acid-based Combined Amendment on Soil Quality in Saline-sodic Farmlands in the West Liaohe Plain, China

Water scarcity and soil salinization pose significant challenges to agriculture in the West Liaohe Plain, eastern Inner Mongolia, China. Shallow-buried drip irrigation can improve soil water use efficiency to alleviate water shortage in agriculture and the application of lignite humic acid reduces the adverse effects of soil salinization. However, further research is needed to investigate the effects of different application rates of lignite humic acid and humic acid-based combined amendment on soil physicochemical properties, nutrient contents, and crop yield in saline-sodic farmlands under shallow-buried drip irrigation. A two-year field experiment was conducted with control without any amendment (CK), three treatments amended with 3 t/ha (H1), 6 t/ha (H2), and 12 t/ha (H3) lignite humic acid, and three application rates with 15 t/ha (T1), 22.5 t/ha (T2), and 30 t/ha (T3) lignite humic acid-based combined amendment in 2021 and 2022. The results showed that H3 reduced soil bulk density, pH, electrical conductivity, and total alkalinity, while increasing the contents of soil organic matter, total nitrogen, and available potassium in the two-year experiment. Moreover, the maize yield in H3 increased by an average of 35.5%. T2 decreased soil bulk density, pH, total alkalinity, and increased maize yield by 16.2%, compared to the first year. These results suggest that T2 consistently improved both soil quality and crop yield. Correlation analyses showed that lignite humic acid and its complexes promote maize growth and increase yield by increasing soil organic matter and total nitrogen while reducing soil salinity and total alkalinity. Based on the comprehensive analysis of the field data and the results of the comprehensive evaluation of soil quality, it was determined that the appropriate improvement measures for saline-sodic farmlands under shallow-buried drip irrigation are the application of 12 t/ha of lignite humic acid and 22.5 t/ha of lignite humic acid-based combined amendment. This study demonstrates the effectiveness of lignite humic acid and its combined amendment in mitigating the constraints of saline-sodic farmlands and enhancing crop yields, providing a sustainable solution for improving saline-sodic farmlands in the West Liaohe Plain.