Effects Of Combined Application Of Organic And Inorganic Fertilizers Plus Dmpp On Nitrogen Transformation And Microbial Activity In Soils

In order to discuss the mechanism of action of DMPP in reducing nitrogen losss in fields, effects of combined application of organic and inorganic fertilizers plus DMPP on nitrogen transformation and the activity of microorgamism in soils were studied. For that end, aerobic thermostat pot experiment, pot experiment of green vegetables, pot experiment of rice and simulated rainfall experment were designed in this paper. The main results obtained are as follows:1. After60days of incubation, it was found that NH4+-N concentration was89times higher and NO3--N concentration57.8%lower in the pots higher in fertilization rate than in the pots conventional in fertilization rate; in the pots subjected to flooding and combined application of organic and inorganic fertilizers plus DMPP, NH4+-N concentration kept on rising and nitrification process was more significantly inhibited; NH4+-N concentration was56times higher and NO3--N concentration18times lower in the pots incubated under15℃than in the pots under25℃, and NH4+-N concentration was30and31times higher and NO3--N concentration was44.3%and66.4%lower in the pots of red soil than in the pots of silt paddy soil and blue clayey paddy soil, respectively. The optimal nitrification inhibitory effect was observed during the period from D30to D40in the pots of blue clayey paddy soil, silt paddy soil and red soil subjected to combined application of organic and inorganic fertilizers plus DMPP under25℃, and inhibitory effect of the treatment may last throughout the experiment period of60days.2. Pot experiment of green vegetables showed that the nitrification inhibitory effect was outstanding in sandy soil, while persistent in loam soil subjected to combined application of organic and inorganic fertilizers plus DMPP. The activity of microorganisms were reduced26.63%and34.78%in blue clayey paddy soil and red soil respectively, but this phenomenon was not observed in silt paddy soil subjected to combined application of organic and inorganic fertilizers plus DMPP. The fresh weight of green vegetable was enhanced2.0%and3.4%, and the dry weight was increased5.1%and7.6%in blue clayey paddy soil and silt paddy soil respectively, meanwhile the content of NO3-N was reduced15.7%,40.8%and40.5%in blue clayey paddy soil, red soil and silt paddy soil respectively, furthermore, the content of TN, TP and TK were totally enhanced subjected to combined application of organic and inorganic fertilizers plus DMPP. 3. Pot experiment of rice showed that the content of NO3--N was reduced34.5%,8.9%and33.0%in blue clayey paddy soil, red soil and silt paddy soil respectively, and the risk of nitrogen loss was reduced subjected to combined application of organic and inorganic fertilizers plus DMPP. The activity of microorganism in long-term rainfed soil was more inhibitoried than that in long-term flooded soil subjected to DMPP. The dry weight of grain was enhanced2.9%,7.0%and11.3%in blue clayey paddy soil, red soil and silt paddy soil respectively, meanwhile the content of TN, TP and TK were totally enhanced subjected to combined application of organic and inorganic fertilizers plus DMPP.4. Simulation rainfall experiments showed that the TN loss decreased by36.4%,50.8%and78.8%respectively in surface soil, and13.1%,4.9%and4.6%respectively in runoff water subjected to combined application of organic and inorganic fertilizers plus DMPP compared to combined application of organic and inorganic fertilizers into the soil. At the same time, DMPP could reduce the conductivity in runoff water; thereby reduce the risk of base cations lossing with runoff water from soil.