Reducing Negative Consequences Of Nitrogen Fertilization Through Dicyandiamide Application On Soil In The Loess Plateau

Nitrogen?N?is indeed the most consumed plant nutrient in the world,essentially required by all plant species for better growth and development.N significance as a key player in environmental degradation increased recently because our agricultural systems are inefficient in N management,which are characterized by reduced N use efficiency?NUE?and excessive N losses in the environment.Gaseous N emissions?NH₃,N₂O,NO?and nitrate?NO₃^--N?leaching are the main N loss pathways,which are direct threats to air and water quality.Soil acidification and CO₂ emission from calcareous soils are other adverse effects of N on ecosystem.Nitrification process,involving the conversion of ammonium?NH₄⁺-N?to NO₃^--N is the precursor of majority of aforementioned N losses from soil,which needs to be controlled in order to overcome N related environment problems.Inhibition of nitrification as a mitigation tool to abate N losses is a promising technology.Therefore,we have studied the efficacy of dicyandiamide?DCD?in inhibiting the nitrification process and reducing N losses via field and incubation experiments.Main results and conclusion of the studies are stated below:1.DCD was evaluated in two consecutive wheat-maize rotations?2015-2017?,at two different N fertilizer levels applied in wheat(160,220 kg N ha^-1)and maize(180,280 kg N ha^-1).More NH₄⁺-N contents?101%and 102%in wheat and 74%and 73%in maize?and less NO₃^--N contents?37%and 43%in wheat and 46%and 57%in maize?were observed at both N levels treated with DCD compared to without DCD.Higher pH,lower EC and reduced NO₃^--N accumulation were the other benefits of DCD.The NO₃^--N accumulation within the 0-200 cm soil profile was significantly less at both N levels with DCD(66 mg kg^-1 and 121 mg kg^-1)compared to without DCD(96 mg kg^-1 and 169 mg kg^-1).Application of DCD also improved the growth and yield in both crops.Increase in NUE from 38%-49%in wheat and 27%-33%in maize with DCD at higher N level was also observed.Overall,the effectiveness of DCD in retarding the nitrification process was higher in wheat than maize.2.The impact of DCD on carbon dioxide?CO₂?emission and ammonia?NH₃?volatilization was also tested through two wheat-maize rotations.The application of N fertilizer decreased soil pH,and increased CO₂ emission and NH₃ volatilization,which increased with increase in the level of N fertilizer.DCD application significantly reduced CO₂ emission in both wheat?10-20%?and maize crops?13-14%?,compared with the N fertilizer without DCD.The losses of NH₃ volatilization increased when DCD was applied at both levels of N fertilizer in wheat?38-41%?and maize?24-36%?crops.3.Substantial amount of mineral N accumulation was noticed in the soil profile?0-200cm?at both levels of N fertilizer with and without DCD.We continued the field experiment for another wheat-maize rotation?2017-2018?,but without any addition of N fertilizer.The results of the chlorophyll contents,yield,and aboveground plant biomass showed significant effect of the residual N,as no difference was observed in aforementioned parameters,when they are compared with the results of previous two years under N fertilization.Crops uptake significant amount of N fertilizer(64 kg ha^-1 in wheat and 120 kg ha^-1 in maize),which was mainly drawn from the residual N accumulated in the soil profile,as we noticed considerable decrease in the mineral N accumulation in soil profile,as well as downward movement of NO₃^--N.4.DCD applied in calcareous soil with N fertilizer(0.2 g kg^-1 soil)was tested for its efficiency to reduce N losses and gaseous emissions through an incubation experiment conducted at two temperature?10 ^oC and 25 ^oC?and two moisture levels?40%and 60%WFPS?.DCD application with N fertilizer effectively reduced the nitrification process,characterized by higher NH₄⁺-N contents and soil pH,and lower NO₃^--N contents and soil EC,when compared with N level without DCD.Inhibited nitrification because of DCD also resulted in decreased emission of N₂O and CO₂ from soil,however an increase in the NH₃ volatilization was observed.Temperature and moisture significantly influenced the nitrification process and gaseous emissions,with maximum rates observed at higher temperature?25 ^oC?and moisture level?60%WFPS?.Results further concluded that the nitrification inhibition was mainly driven by the availability of DCD contents in soil.DCD was least effective to inhibit nitrification process and reduce N₂O and CO₂ emission from soil at 25 ^oC and 60%WFPS,which was significantly correlated with its highest degradation and lowest concentration at the same temperature and moisture level.