Effects Of Nitrogen Fertilizer,biochar And NBPT On Soil Ammonia Volatilization And The Abundance Of Related Genes

Ammonia is the most important gaseous alkaline pollutant in the atmosphere,mainly from agriculture and animal husbandry.Soil ammonia volatilization is also the main way of soil nitrogen loss,among which NH₃ emission caused by nitrogen fertilizer application in farmland accounts for 40%of agricultural emission sources.Unreasonable fertilizer input and unscientific fertilizer application methods lead to problems such as low nitrogen utilization rate（26.1%-28.3%）and ammonia volatilization,resulting in a series of economic losses and environmental hazards.Therefore,it is of great practical significance to adopt effective ways to improve the utilization rate of urea nitrogen and reduce the loss of nitrogen.In this experiment,the summer corn-wheat rotation cropland was used as the research object,and a split-plot experimental design was used to study urea（N0,N75,N150,N225 and N300 kg N ha-1）,biochar（BC 0 and BC7）under field conditions.5 Mg Cha-1)and urease inhibitors（NBPT 0%and NBPT2%）combined with the effects on soil ammonia flux and functional genes controlling urea hydrolysis and nitrification,which provided information for the control of nitrogen loss in local farmland.Theoretical and technical basis.During the experiment,soil ammonia volatilization,soil moisture,temperature,p H,soil NO3-,NH4+,urease activity（UA）,and abundance of N cycle-related genes（urease gene ure C,ammonia oxidizing bacteria gene amo B）were monitored every 5-15 days.and ammonia-oxidizing archaeal gene amo A).The main results are as follows:（1）The rate of soil ammonia volatilization and the total amount of ammonia volatilization increased with the increase of N dosage.Soil ammonia volatilization flux was significantly negatively correlated with nitrate nitrogen（P<0.01）,and extremely significantly positively correlated with soil temperature（5cm）（P<0.01）.NBPT reduced the rate of ammonia volatilization,and the inhibitory effect began after one week of basal fertilizer weaken.Biochar increased the ammonia volatilization rate within one week after the basal fertilizer,but exhibited an inhibitory effect on the average ammonia volatilization rate throughout the growth period.（2）The total amount of soil ammonia volatilization varies with years and types of crops.The total amount of soil ammonia volatilization in the second year rotation(30.26-34.57 kg N ha^-1)was higher than that in the first year rotation(20.68-30.97 kg N ha^-1);The average total soil ammonia emissions in the wheat season(15.18-17.15 kg N ha^-1)were higher than those in the corn season(10.30-13.12 kg N ha^-1).（3）The p H value decreased with the increase of nitrogen dosage,and the EC value,nitrate nitrogen content and ammonium nitrogen content increased with the increase of nitrogen dosage.The p H value and EC value,nitrate nitrogen content and ammonium nitrogen content throughout the experimental period within one week after the biochar was added to the basal fertilizer.NBPT increased p H within one week after fertilization and decreased EC,nitrate nitrogen content and ammonium nitrogen content within one week after fertilization.（4）Urease activity and gene abundance increased with the increase of N dosage;NBPT decreased urease activity,ure C and amo B gene abundance,but increased amo A gene abundance;biochar increased urease activity,amo A and amo B gene abundance.degree,reducing the ure C gene abundance.Urease activity was significantly positively correlated with ammonium nitrogen content,soil temperature（5 cm）and water content（0-10 cm）.The abundance of ure C is greater than that of amo B,and amo B is three orders of magnitude higher than amo A.The abundance of ure C gene was significantly positively correlated with urease activity（P<0.05）,extremely significantly positively correlated with amo B,nitrate nitrogen and ammonium nitrogen content（P<0.01）,and extremely significantly negatively correlated with p H（P<0.01）;amo B,amo A gene abundances of nitrate nitrogen,ammonium nitrogen,soil temperature were extremely significantly positively correlated（P<0.01）,and extremely significantly negatively correlated with p H（P<0.01）;amo B was extremely significantly positively correlated with amo A.In conclusion,temperature is the main controlling factor of soil ammonia volatilization.Biochar or NBPT mediates the transformation process and ammonia volatilization loss in soil by affecting soil p H,gene abundance,nitrate nitrogen content,ammonium nitrogen content,urease activity,and urea hydrolysis.The effect mechanism of biochar and NBPT on ammonia volatilization is as follows:NBPT alleviates NH3 by affecting ure C and reducing UA,and biochar has a synergistic effect with NBPT by increasing the abundance of amo B and amo A and enhancing nitrification.