DMPP Inhibition Mechanism And Its Interaction Effects With Chromium Or Cadmium On Nitrogen Transformation In Soil

DMPP (3,4-Dimethylpyrazole phosphate) is a new effective nitrification inhibitor, andthe study of DMPP nitrification inhibitor effects and its mechanism, as well as its effects onsoil nitrogen transformation in different soil types and heavy metal polluted soils plays animportant role in agricultural production application and environmental protection. In thispaper, pot and simulating experiments were conducted to study DMPP nitrification inhibitionmechanism and its effects on soil nitrogen transformation, growth and yield of wheat inJiangxi Krasnozems soil and Yangling Loess soil. The inhibition mechanism was studied bymeasuring soil enzyme activities and microbial population changes.The main conclusions are as follows:1. Nitrification inhibitor DMPP had a stronger inhibition effect on ammonia oxidation incalcareous soil, and could significantly inhibit the accumulation of soil nitrite nitrogen. Therewas no significant difference among different concentrations of DMPP treatments. Therecommended DMPP rate in carcalous soil was0.5%of pure nitrogen.2. Amended DMPP in soil significantly decreased the mean population ofammonia-oxidizing bacteria (AOB), but had no effect on the population of nitrite-oxidizingbacteria (NOB). Amended DMPP in soil significantly decreased the activities of urease andnitrate reductase (NaR); low contents (≤1%) of DMPP had no effect on hydroxylamineoxidoreductase (HAO) activity. Therefore, these results indicated that applied DMPP coulddecrease NO2--N accumulation and NO3--N leaching by inhibiting AOB population growthand by inhibiting the oxidation of ammonia into hydroxylamine instead of the oxidation ofhydroxylamine into nitrite.3. Applied DMPP in Jiangxi Krasnozems soil and Yangling Loess soil couldsignificantly decrease soil nitrate reductase and increase ammonium nitrogen contents. Theapplication of DMPP in the two kinds of soil could significantly inhibit bacterial metabolicactivity and species diversity; it could decrease urease activity in Loess soil, but had nosignificant effect on soil urease activity in Krasnozems soil. Reflected in the biologicaleffects, applying DMPP in Loees soil could significantly increase plant height and biomass in seedling and jointing stage, and could increase the kernel weight of wheat, but had noinfluence on nitrogen and phosphorus in seeds. In Krasnozems soil, DMPP could increase theyield, kernel weight of wheat, nitrogen and phosphorus content in grains, but had nosignificant effect on potassium content in grains.4. In the test concentration, Cr significantly inhibited the bacterial metabolic activity butincreased species diversity, and increased soil NaR activity and decreased the activity ofurease; as a result, it increased the content of soil nitrate and promoted the nitrificationprogress. Cr in soil had no effect on the yield of wheat, nitrogen and potassium content ingrains; while it increased the CAT activity and MDA content in wheat. Cd could reduce theactivity of soil urease, had no effect on nitrification and soil NaR activity. Cd couldsignificantly decrease the kernel weight of wheat, and increase the content of grainphosphorus, but it had no effect on wheat yield, grain nitrogen and potassium content inwheat.5. Under the interaction of DMPP and Cr, the diversity of bacterial community and soilnitrate content was lower than Cr alone but higher than DMPP alone, it indicated that Crcould weaked the nitrification inhibition effect of DMPP. Under the interaction of DMPP andCd, the nitrification inhibition effect of DMPP was not influenced by Cd, but the DMPPinhibition on soil microbial diversity was more obvious. Amended DMPP could significantlyreduce the transport coefficients of heavy metals Cr and Cd in wheat, and increased Cr andCd enrichment in root.6. The application of the exogenous Cr (III) and Cr (VI) could significantly increase soilammonium nitrogen content which increased with the concentration of Cr. Cr (III) at theconcentration of50~225mg·kg-1could improve the nitrification in prophase of cultivation,and had the biggest improvement at150mg·kg-1. But in all Cr (VI) treatments, thenitrification in soil was inhibited, and the inhibition increased with increasing concentrationof exogenous Cr (VI).