Coupling effects of biostimulant application and planting density for synergistic enhancement of sorghum and amelioration of saline-alkali soil

Abstract

A randomized block experiment was conducted to investigate combined effects of planting density and biostimulants on sorghum performance and saline-alkali soil properties. Treatments included two densities (S, C) and three biostimulant applications: CK (control), sole γ-aminobutyric acid (T1), and γ-aminobutyric acid plus microbial inoculants (T2). The findings demonstrated that density-biostimulant interactions significantly affected sorghum agronomic traits and soil physicochemical properties. CT2 reduced soil pH, electrical conductivity by 18.30%, and bulk density by 16.46%, while increasing soil organic matter by 19%. Soil enzyme (N-acetyl-β-D-glucosaminidase, β-glucosidase, Leucine aminopeptidase, Alkaline phosphatase) activities showed distinct temporal dynamics: CT2 peaked at grain filling, whereas CK dominated at maturity stage. Furthermore, compared with CK, CT2 markedly increased plant height by 18.99%, stem diameter by 35.10%, leaf area by 67.49%, total dry matter by 25.86%, and dry matter partitioning to spikes by 37.03%. It also raised thousand-kernel weight by 33.49% and grains per spike by 51.65%, thereby improving grain yield by 6.00%. By comparison, ST1 yielded a striking 55.02% increment in grain yield. Altogether, these findings implied that under saline-alkali stress, dual biostimulants at low density benefit soil and single plants, and γ-aminobutyric acid at high density boosts population yield, showing individual-population yield tradeoffs.