Integration of Organic-Inorganic Nitrogen Fertilization on Nitrogen Conversion in Soil

Akhlaq Ahmad^1*Aaqil Khan²Farhan Ullah¹Muhammad Ahmad Hassan¹Javed Iqbal¹Jun Wang¹He Song¹Zhaorong Dong^1*

• ¹Anhui Agricultural University, Anhui, China
• ²Guangdong Ocean University, Zhanjiang, China

The integration of organic and inorganic nitrogen fertilization significantly impacts soil nitrogen conversion, microbial dynamics, promoting sustainable soil health and enhancing crop productivity. Excessive inorganic fertilizer use causes environmental issues like nitrate leaching and greenhouse gas emissions, while organic fertilizers enhance soil microbial activity and long-term fertility. This study evaluates the combined effect of organic (sheep manure) and inorganic nitrogen fertilization on soil and plant nitrogen dynamics, microbial activity and greenhouse gas emissions, hypothesizing that integration would improve soil health and reduce environmental impacts. A field experiment over one maize growing season, employed a randomized block design with six treatments: no fertilizer (T1), chemical fertilizer only (T2), 15% (T3), 30% (T4), or 45% (T5) sheep manure combined with chemical fertilizer, and sheep manure only (T6). Soil samples were analyzed for pH, dissolved organic carbon (DOC), nitrate (NO3 -), ammonium (NH4 +), and microbial gene abundance (AOA, AOB, nirK, nirS). The treatment T6 (100% sheep manure) showed significantly higher contents in soil DOC (34 ± 4.58 mg/kg) and NO₃⁻ (3.31± 0.51 mg/kg) concentrations promoting microbial diversity and activity. The inorganic only treatment (T2) showed highest grain nitrogen content (9.43 ± 2.24 mg/kg), highlighting immediate nutrient availability. The integration of organic and inorganic fertilizers optimized nutrient cycling, enhanced microbial functions, and reduced environmental impacts. Heat map and PCA analyses revealed distinct responses of AOA, AOB, nirK, and nirS gene expressions to different fertilization treatments, with high organic inputs fostering a diverse and active microbial community. RDA showed strong correlations between environmental factors and gene expression, emplacing the role of integrated fertilization in maintaining soil health. Moreover, organic and inorganic fertilizer integration, optimized nutrient cycling, enhanced microbial functions, and reduced environmental impacts. Organic fertilization fosters a microbial community, enhancing nitrification and denitrification. These results suggested that integrating organic and inorganic fertilization improves soil health, supports sustainable agriculture, and enhances crop productivity, reducing nitrate leaching and greenhouse gas emissions.