A deep placement of lime nitrogen reduces the nitrate leaching and promotes soybean growth and seed yield

Deep placement of coated urea, lime nitrogen (Lime N), or urea with a nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP-U) did not inhibit N fixation activity, and it promoted soybean growth and seed yield. However, the effect of deep placement on the N budget including N leaching has not been evaluated. In this research, soybean plants were cultivated with a basal deep placement of urea, Lime N, or DMPP-U, and the control without deep placement of N fertilizer in lysimeters filled with Andosols. The nitrate was the principal N leachate and most of them leached until the flowering stage. The total amount of leached nitrate was the highest in urea deep placement, and it was reduced by the deep placement of Lime N or DMPP-U. In 2020, the total amount of nitrate in the leachate during the cultivation was 0.95, 1.83, and 2.78 ​g ​N m⁻² in control, Lime N, and urea, respectively. The seed yield was higher in Lime N (424 ​g ​m⁻²) and urea (399 ​g ​m⁻²) than in the control (267 ​g ​m⁻²). The total amount of N accumulated in the shoots was higher in Lime N (32.1 ​g ​N m⁻²) than in the control (26.5 ​g ​N m⁻²) and urea (24.2 ​g ​N m⁻²) treatments. These results indicated that soybean plants with Lime N might assimilate more N both from N fertilizer and N₂ fixation compared with control plants. Soil incubation test confirmed that the Lime N or DMPP-U retarded nitrification than urea.