Effects of deep fertilization placement on N2O emissions, nitrogen leaching and soybean productivity

Purpose: Crops growth in upland fields converted from previously used as rice paddies is often limited by poor drainage, which decreases nitrogen (N) fertilizer use efficiency due to increased nitrous oxide (N 2 O) emissions.Deep fertilizer placement is well established as a strategy to promote root growth and yield and reduce N 2 Oemissions.However, its effects on paddy-to-upland converted soils remain unknown.This study investigated the effects of the deep placement of inorganic fertilizer and organic mixtures (compost and biochar) on soybean root development, yield, N leaching, and N 2 O emissions in paddy-to-upland converted soils.Methods: Soil-plant column experiments with four treatments were established based on placement depth of fertilizer and organic mixture: Surface Inorganic and Surface Organic (SISO); Deep Inorganic (10 cm) and Deep Organic (20 cm) (DIDO), Surface Organic and Deep Inorganic (20 cm) (SODI), and Surface Inorganic and Deep Organic (20 cm) (SIDO).Each treatment had ten replicates, and soybeans were cultivated.During the experiment, N 2 O emissions and N leaching were measured, and soybean roots and yields were determined at the harvest.Results: Soybean root development was most pronounced in DIDO treatment, which showed significantly greater root length, volume, and surface area than the other treatments, resulting in the greatest soybean growth and yield.Nitrogen leaching amounts did not differ among the treatments.However, N leaching relative rate was greatest in SODI (by 60.4%), while DIDO had smaller one (12%).Cumulative N 2 O emissions were significantly affected by placement depth, with the greatest emissions in SISO and the smallest in DIDO.Conclusions: These results indicate that placing both organic and inorganic nutrient sources deep in the soil profile enhances root development and yield while simultaneously reducing nitrogen loss and N 2 O emissions, offering an effective management strategy for soybean cultivation in paddy-converted soils.