Nitrogen transformation and plant growth in response to different urea-application methods and the addition of DMPP

The differences in soil inorganic-nitrogen (N) concentration and distribution, plant biomass, and root growth in the presence or absence of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) under different urea-application methods (placement versus homogeneously applied) were explored in a short-term microcosm experiment. Spring wheat (Triticum aestivum L.) was grown in a microcosm with six different treatments: no amendment (CK), DMPP homogeneously applied (DMPP-hom), urea homogeneously applied (Urea-hom), urea with DMPP homogeneously applied (Urea + DMPP-hom), urea placement (Urea-place), and urea with DMPP placement (Urea + DMPP-place). After 28 d, plant biomass, soil inorganic nitrogen content, distribution of soil inorganic nitrogen and plant roots in the soil were analyzed. The soil inorganic N and plant roots tended to be distributed asymmetrically in the placement treatment but were distributed symmetrically in the homogeneous treatment. DMPP addition significantly increased the soil NH4+-N content and decreased the NO3--N content, especially near the fertilized zones in the placement treatment. Compared to the urea-only treatments, DMPP application significantly increased the shoot biomass and root lengths of the wheat in the homogeneous treatment but decreased them in the placement treatment. Therefore, homogeneously applied urea and DMPP may produce a more uniform nutrient distribution, leading to greater nitrogen retention in the soil and thus accelerating wheat growth.