The Effect of Organic and Inorganic Nitrogen Combined Application on Photosynthesis and Antioxidant Characteristics of Corn in Salt-Affected SoilsA Sustainable Fertilization Strategy to Boost Maize Yield and Photosynthetic Resilience in Saline Soils

Hui Zhou¹Jiawei Guo²Yongqiang Wang^2*Hui Zhou¹Hu Liu^1*

• ¹Yinshanbeilu Grassland Eco-Hydrology National Observation and Research Station, China Institute of Water Resources and Hydropower Research, China Institute of Water Resources and Hydropower Research, Beijing, Beijing Municipality, China
• ²Inner Mongolia Agricultural University, Hohhot, Inner Mongolia Autonomous Region, China

Soil salinization is a major constraint to crop production in arid and semi-arid regions. In recent years, the combined application of organic and inorganic nitrogen (OIN) has been recognized as an effective strategy for enhancing the productivity of saline soils. However, limited studies have explored the yield improvement mechanisms from the perspective of photosynthetic performance and antioxidant responses. From 2018 to 2020, a field experiment was conducted in the Hetao Irrigation District of Inner Mongolia using mildly saline soil (S1, EC = 0.68 dS m-1) and moderately saline soil (S2, EC = 1.25 dS m-1). Six treatments were established: no nitrogen application (CK), inorganic nitrogen only (U1), and organic nitrogen replacing 25%, 50%, 75%, and 100% of the inorganic nitrogen (U3O1, U1O1, U1O3, and O1, respectively). The effects of OIN application on maize growth (plant height, leaf area index, biomass, chlorophyll content, and yield), photosynthetic parameters (net photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO₂ concentration), and antioxidant enzyme activities (superoxide dismutase [SOD], catalase [CAT], and peroxidase [POD]) were investigated. Results showed that under S1 conditions, OIN significantly improved LAI and photosynthetic performance, enhanced SOD activity, and increased yield, with U1O1 producing the highest yield. Under S2 conditions, maize growth and photosynthetic parameters were significantly reduced compared to S1, while malondialdehyde (MDA) content and antioxidant enzyme activities were significantly elevated. OIN application markedly improved growth performance, photosynthetic efficiency, and CAT activity, with O1 achieving the highest yield. Structural equation modeling revealed that under S1, yield improvement was primarily driven by enhanced photosynthetic traits, whereas under S2, growth characteristics, photosynthetic capacity, and CAT activity jointly contributed to yield formation. Overall, OIN application effectively mitigated the inhibitory effects of salinity stress on maize growth, with U1O1 and O1 being the optimal treatments for mildly and moderately saline soils, respectively.