Effects of stabilized urea containing NBPT/DMPP/CP on nitrogen use efficiency and maize yield in black and cinnamon soil

Objectives The effect of commonly used N fertilizer synergistic agents were studied in black soil and cinnamon soil, aiming to identify the suitable type of urease and nitrification inhibitors for the two soils.

Methods The tested synergistic agents included N-butyl thiophosphate-triamine (NBPT), 3, 4-dimethyl-pyrazole phosphate(DMPP), and 2-chloro-6 (trichloromethyl)-pyridine (CP). A pot experiment was conducted using maize as test materials. Besides no N control, seven treatments were set up, they were urea (U), and U plus NBPT, DMPP, CP, NBPT+DMPP, NBPT+CP, and DMPP+CP. The contents of urea N, NH₄⁺-N and NO₃^–-N in soil were measured at seedling, big trumpet, grouting and maturity stage of maize, and the nitrification inhibition rate was calculated correspondingly. The maize leaf area and chlorophyll content were measured after tassel spinning, and the biomass and N content of the plant were measured after harvest.

Results 1) Compared with common urea treatment, adding NBPT+DMPP and NBPT+CP treatments increased the content of NH₄⁺-N in black soil by 1.32 and 0.96 times, and decreased the content of NO₃^–-N by 1.35 and 1.04 times in the seedling stage of maize. The leaf area of corn and the content of chlorophyll were increased because the sufficient soil NH₄⁺ supply. In cinnamon soil, DMPP+CP increased the content of NH₄⁺-N by 3.09 times compared with U treatment, and decreased the content of NO₃^–-N by 1.49 times. Meanwhile, the content of chlorophyll increased by 1.61 times, higher than that in control and single inhibitor treatment significantly. 2) In black soil, the grain yield of NBPT+DMPP and NBPT+CP was increased by 1.64 and 2.18 times, respectively, compared with U treatment. The N apparent use efficiency increased by 3.02 and 3.34 times, which were higher than those in other treatments (P < 0.05). DMPP+CP increased the grain yield and the N apparent use efficiency in cinnamon soil by 1.41 times and 4.98 times, respectively, which were higher than those in other treatments.

Conclusions In black soil, NBPT+DMPP and NBPT+CP exhibited highest yield, inhibited nitrification and increased N absorption by maize and the N apparent use efficiency. In cinnamon soil, the combining addition of DMPP+CP significantly decreased nitrification rate than any single inhibitor application, reduced N loss and increased N uptake of maize, leading to a high yield of corn. Therefore, adding DMPP+CP is the best choice for stabilized urea for corn plantation system in the cinnamon soil.