Objectives The production of the polymer saline-alkali soil amendment carboxymethyl cellulose-polyacrylamide (CMC-PAM) from corn straw generates a large amount of acidic by-products, creating a need for their resource utilization. This study investigated the effects of co-application of CMC-PAM and acidic by-products on the improvement of sodic saline-alkali soil, providing a theoretical basis for the recycling and utilization of these by-products.

Methods Cellulose derived from corn straw using different acid hydrolysis methods and the corresponding CMC-PAM products prepared by grafting acrylamide were structurally characterized. The chemical compositions of CMC-PAM and the acidic by-products were also analyzed. Pot experiments with rice grown in sodic saline-alkali soil were conducted in 2023 and 2024. In 2023, three treatments were established: gypsum control (CK); gypsum + CMC-PAM (OPT1); and gypsum + CMC-PAM + acidic by-products (OPT2). In 2024, a gypsum + cellulose treatment (OPT3) was added in addition to the above three treatments. Soil samples were collected at the tillering and maturity stages to determine soil pH, electrical conductivity (EC), exchangeable sodium percentage (ESP), and water-soluble ion contents. At maturity, plant samples were collected to determine rice yield and yield components.

Results 1) Compared with CMC-PAM prepared using the hydrochloric acid/nitric acid mixed hydrolysis method in 2023, CMC-PAM prepared using sulfuric acid in 2024 exhibited a more developed surface pore structure with a more uniform distribution. The acidic by-products generated during preparation were rich in nutrients, including soluble organic carbon, phosphorus, and potassium. 2) Compared with CK, the combined application of CMC-PAM and acidic by-products significantly reduced soil pH, EC, ESP, and water-soluble ion contents at both the tillering and maturity stages. Specifically, at maturity, OPT2 decreased soil pH by 0.35–1.40 units, reduced EC by 51.60%–61.70%, decreased water-soluble Na⁺ content by 19.18%–78.70%, and significantly increased water-soluble Ca²⁺content. Several soil improvement indicators were also significantly better in OPT2 than in OPT1. 3) Application of CMC-PAM alone or in combination with acidic by-products promoted rice tillering and increased dry matter accumulation, nutrient uptake, and grain yield. Compared with CMC-PAM alone (OPT1), the combined application of CMC-PAM and acidic by-products (OPT2) increased rice tillering and dry matter accumulation. Compared with CK, OPT2 increased total nitrogen, phosphorus, and potassium accumulation at maturity by 43.47%–51.13%, 58.67%–123.42%, and 122.43%–135.93%, respectively. In addition, the number of grains per panicle increased by 7.18%–28.77%, and grain yield increased significantly by 39.96%–56.47%.

Conclusions The combined application of CMC-PAM and acidic by-products significantly enhanced the improvement effect of gypsum on sodic saline-alkali soil. The acidic by-products contributed to soil alkalinity neutralization and displacement of exchangeable sodium from soil colloids, while CMC-PAM facilitated the adsorption and retention of nutrients such as Ca and Mg. Consequently, this combined amendment reduced soil pH, EC, and ESP while improving nutrient availability and promoting rice growth. The joint application of corn straw-derived CMC-PAM and its acidic by-products not only enables straw resource utilization and enhances gypsum-based soil remediation but also reduces waste disposal costs, providing an efficient resource recycling strategy for improving saline-alkali soils in Northeast China.