Evaluations of the DMPP on organic and inorganic nitrogen mineralization and plant heavy metals absorption

•DMPP added to the combined fertilizers extended the soil ammonium retention.•DMPP greatly reduced the soil nitrate and nitrite contents in combined fertilization.•DMPP impacts on heavy metal uptake related with nitrate counterion effect and soil pH.•DMPP reduced the plant uptake of Cu, Zn and Cd in the soil.

The use of biochemical technologies to regulate soil nitrogen (N) transformations is an important strategy to improve plant nutrient uptake and its quality. Effect of organic and inorganic N fertilizers combined application supplemented with the nitrification inhibitor 3,4-dimethyl pyrazole phosphate (DMPP) on N transformations in the soil and heavy metal uptake of pakchoi cabbage (Brassica campestris L. ssp. chinensis) was studied in three different kinds of soils (purplish clayey soil, red soil, and sandy loam soil). The results demonstrated that DMPP addition in the organic and inorganic N combined fertilization extended ammonium N retention, and greatly reduced nitrate and nitrite N concentrations in three soils. Compared to the regular organic and inorganic-N combined fertilizers, DMPP addition in this fertilization increased the pakchoi biomass by 9.8% to 15.8% and reduced its nitrate concentrations by 15.7% to 40.8%. Furthermore, DMPP addition in the combined organic and inorganic fertilization decreased the heavy metal content of Cu (7.8% to 25.6%), Zn (10.4% to 20.3%), and Cd (12.8% to 22.2%) in the plant. The addition of DMPP to the organic and inorganic-N combined fertilizers could decrease the heavy metal counterion nitrate uptake in the plant, alter soil pH and decrease the activity of Cu, Zn and Cd in the soil, and weaken the plant heavy metal uptake of Cd and Zn in the three soils. It is proposed that DMPP could be used to regulate N transformation in the soil and decrease the heavy metal content in the plant in the organic and inorganic N combined fertilization, thus improving plant quality and yields.