Vermicompost and Azotobacter chroococcum amendment of saline-alkali soil decreases nitrogen loss and increases nitrogen uptake confirmed by ZmNRT1.1B of maize

Abstract

Globally, enhancing nitrogen (N) retention and optimizing N utilization efficiency in saline-alkali soils are crucial for sustainable agricultural practices and food security. This research aims to address the challenges of significant N loss and suboptimal N utilization efficiency in maize planted in saline-alkali soil. Employing soil column cultivation assays and maize lines with a ZmNRT1.1B loss-of-function mutation, we investigated the impacts of vermicompost and Azotobacter chroococcum on N loss mechanisms (including NH₃ volatilization and ¹⁵N leaching) and therefore maize N uptake efficiency. The results showed that combined application of vermicompost and A. chroococcum reduced total NH₃ volatilization by 35.0 % through lowering pH and Na⁺ levels, and enhanced cation exchange capacity (CEC). Additionally, this treatment increased soil organic carbon (SOC) content and promoted the formation of macroaggregates, thereby reducing ¹⁵N leaching into deeper soil layer by 35.0 %–48.0 %, which led to the increase of soil available ¹⁵N by 7.91 %–8.84 %. Furthermore, this amendment enhanced the shoot and root biomass by 88.0 % and 45.2 %, respectively, and increased the total N uptake by 36.7 % of wild-type maize, likely due to increased soil available N and a reduced Na⁺/K⁺ ratio in root. The improved ¹⁵N uptake in maize was linked to the activation of the ZmNRT1.1B gene, as evidenced by the growth inhibition and reduced N uptake in maize with a ZmNRT1.1B loss-of-function mutation. Collectively, vermicompost and A. chroococcum mitigate N loss in saline-alkali soil, thereby increasing stored available N and promoting N uptake and maize growth. These strategies significantly improve the effective management and utilization of sustainable N resources in saline-alkali soils.