Effects Of Walnut Green Husk On Soil Nitrogen Transformation

Walnut is one of the characteristic agricultural product of Shanxi,and the planting area is 400,000 ha.A lot of walnut green husk were produced every year.Walnut green husk is a thick layer of green peel outside unripe walnut.Its main ingredient contains the naphthoquinone and its glycosides,flavonoids and glycosides,two aryl heptane,terpenoids,organic acids and a series of compounds.The allelopathy effects of walnut green husk can inhibit soil nitrification and reduce the N2 O emission of nitrogen oxides.In addition,walnut green husk can increase the contents of organic matter.In this paper,the inhibitory effect of walnut green husk,cyanide(DCD)and neem powder on the nitrification of nitrogen was studied by simulating soil culture test,the effects of them on nitrogen nitrification were compared,and the mechanism of walnut green husk in the enzymatic and microbiological inhibition mechanism were explored.It aimed to provide scientific basis for walnut green husk as a kind of biological nitrification inhibitor.The results showed that:1 Appling walnut green husk can significantly decrease the content of NO3--N and enhance the fixation of NH4+-N during the urea transformation process in soil.Compared with the control treatment,the content of NO3--N decreased by 46.26% and 57.89% and NH4+-N increased by 370.05% and406.46% when applying 0.5 g and 1 g walnut green husk per 1kg soil.Walnut green husk has the roles of inhibiting urease activity and improving nitrate reductase activity and nitrite reductase activity in soil.There were significant differences between the treatments.Compared with the control treatment,the urease activity decreased by 9.04% and 15.73%,and the nitrate reductase activity increased by 20.30% and 73.81%,and the nitrite reductase activity increased by 12.37% and 40.82%.The dose of 1 g walnut green husk per 1kg soil was perfect.2 Walnut green husk,DCD and neem powder inhibited the oxidation fromNH4+-N to NO3--N,decreased the content of NO3--N in soil,and enhanced the fixation of NH4+-N in the soil.Compared with the control treatment,the content of NO3--N decreased by 58.50%,66.92% and 55.30%,and the content of NH4+-N increased by 428.57%,814.28% and 289.10%.Walnut green husk,DCD and neem powder inhibited soil urease activity,improved soil nitrate reductase activity and nitrite reductase activity.Compared with the control treatment,the activities of urease decreased by 2.83%,10.42%and 8.34%,the activities of nitrate reductase increased by 25.79%,77.79%and 17.07%,and the activities of nitrite reductase were increased by 32.10%,53.91% and 26.32%.The inhibition effect is DCD> walnut green husk>neem powder.3 Walnut green husk,DCD and neem powder applied in soil significantly controlled the oxidation of ammonia growth in the soil and promoted the propagation of denitrifying bacteria.In the early of the experiment,there were significant differences between the treatments,the effect of DCD>walnut green husk>neem powder.Compared with the control treament,the number of ammonia-oxidizing bacteria decreased by 93.15%,93.55% and91.71%,and the denitrifying bacteria increased by 673.33%,1040.72% and464.44%.There were no significant differences in the treatments.