Synergistic effects of nitrogen, sewage sludge, and poultry manure on integrative fertilization for wheat and sugar beet in marginally saline soil

Abstract

Introduction Soil salinity is a major constraint to agricultural productivity in arid and semi-arid regions, affecting approximately 1.4 billion hectares globally (over 10% of the world’s land area) and causing substantial yield losses in staple crops, with reductions reaching up to 50% or more in sensitive species under moderate salinity levels. Methods While the individual effects of biofertilizers or organic amendments have been widely studied, there remains a critical gap in field-based evidence regarding their synergistic integration—particularly the combined use of dual nitrogen (N 2 )-fixing plant growth-promoting rhizobacteria ( Azotobacter chroococcum and Azospirillum lipoferum ) with a balanced blend of sewage sludge and poultry manure (1:1 on N basis) as a 50% substitution for inorganic N in marginally saline soils. This study aimed to evaluate the effects of such integrated fertilization on soil health, nutrient availability, physiological performance, and productivity of wheat ( Triticum aestivum L. cv. Sakha 93) and sugar beet ( Beta vulgaris L. cv. Kawemira) in marginally saline soil (initial EC e 3.47 dS/m). A strip-plot field experiment with five treatments was conducted: control (T1), biofertilizer alone (T2), 50% inorganic N + 50% organic manure (T3), biofertilizer + T3 (T4), and conventional NPK (T5). Soil and plant parameters were assessed at 70 days after sowing (DAS), with final yield and quality parameters determined at harvest. Results and discussion Treatment T4 significantly improved soil organic matter (23.3 g/kg in wheat and 22.9 g/kg in sugar beet), reduced EC e (to 3.90 dS/m in wheat and 3.13 dS/m in sugar beet), and enhanced available N (up to 63.0 mg/kg) and potassium. It also increased microbial biomass carbon, soil enzyme activities, photosynthetic rate (14.0 µmol CO 2 /m 2 /s in wheat and 26.5 µmol CO 2 /m 2 /s in sugar beet), and alleviated salinity-induced stress indicators. The highest yields were recorded under T4, with wheat grain yield reaching 6719 kg/ha and sugar beet root yield 78.8 tons/ha, accompanied by superior sugar quality. These results demonstrate that the integration of dual PGPR with blended organic amendments (T4) offers a synergistic, low-input strategy that enhances soil fertility, mitigates salinity stress, and boosts crop productivity while reducing inorganic fertilizer use by 50%. This approach provides a scalable and sustainable solution for marginally saline soils in arid regions, supporting food security with a reduced environmental footprint. Further multi-site and multi-year validation across a wider range of salinity levels and soil types is recommended.