Nitrogen (N), phosphorus (P), and potassium (K) are considered among the most important essential macronutrients for plants and play fundamental roles in plant growth, yield, and product quality. The vertical movement of nitrate beyond the root zone, which was simulated to a depth of 30 cm in this study, is one of the primary factors contributing to groundwater contamination and the incidence of eutrophication in surface waters. In addition, improper fertilizer management under localized irrigation systems may intensify nutrient losses and reduce fertilizer use efficiency. In the calcareous soils utilized in this research, characterized by a loam texture, the behavior of these elements under the application of liquid fertilizers and drip irrigation has not been fully elucidated. This study was conducted with the objective of determining the optimal dilution ratio for a complete NPK liquid fertilizer and investigating the vertical dynamics of nitrate, phosphorus, and potassium in calcareous loam soil. The fertilizer used in this research was a base commercial liquid fertilizer under the brand name “Vahishta”.



The experiment was designed as a factorial experiment within a completely randomized design, with three replications, using soil columns (35 cm in height and 2.8 cm in diameter). The study was carried out in the Soil Fertility Laboratory of Sari University of Agricultural Sciences and Natural Resources in 2024 (1403 Solar Hijri). The treatments comprised four dilution levels of the complete NPK liquid fertilizer (Control, 1:5, 1:10, and 1:20 fertilizer to water) and three soil depths (0 to 10 cm, 10 to 20 cm, and 20 to 30 cm). The soil exhibited a loam texture, a pH of 7.7, and a high calcium carbonate content. Irrigation was performed in three stages, with the first stage being the only one accompanied by fertilizer application. Soil moisture was maintained at 60% of saturation in order to simulate conditions close to practical field irrigation management. After each irrigation stage, drainage water was collected and analyzed, and soil samples from different depths were separately evaluated for nutrient distribution.



Following the separate analysis of the water drain from each stage and the soil from each layer, the results indicated that at a 1:5 dilution, 48% of the soluble nitrate was transported to the 30 cm depth during the first irrigation stage. In contrast, this amount decreased to 18% in the 1:10 dilution, equivalent to a 62% reduction compared to the 1:5 treatment. Phosphorus demonstrated very low mobility, with over 92% of it being fixed in the 0 to 10 cm soil layer, which is consistent with the strong adsorption and precipitation reactions of phosphorus in calcareous soils. Potassium exhibited moderate mobility and, unlike nitrate, was associated with a relatively uniform distribution throughout the soil profile (0 to 30 cm). The 1:10 dilution ratio established the best balance between the availability of nutrients for potential plant uptake at depth and the reduction of nitrate efflux from the 30 cm depth. These findings indicate that fertilizer dilution plays a decisive role in controlling nutrient transport and minimizing environmental risks.



Therefore, the application of the complete NPK liquid fertilizer at a 1:10 dilution ratio within a drip irrigation system is recommended as a practical strategy for optimal nutrient management, improved fertilizer efficiency, and reducing the risk of water source pollution in the calcareous soils of Iran’s arid and semi-arid regions.