Research Of Black Soil Nitrogen Transformation And Utilization In Maize Under No-tillage

Conservation tillage is the widely promoted tillage practice in Northeast China which has good economic benefits and also good for environment.Our study was based on the conservation tillage experiment site in black soil.We combined the in-situ incubation study,lab analysis and field microplot experiment to clarify the response of soil nitrogen conversion factors?Soil physical and chemical properties,nitrogen transformation microbes,nitrogen transformation rate?under no-tillage,which could provide theoretical basis for rational fertilization,increasing yield,reducing environmental pollution,optimizing black soil management and sustainable agricultural development.?1?Soil nitrogen pool was affected by the tillage practices,Compared with MP,NT significantly?p<0.05?increased total nitrogen?TN?,particle organic nitrogen?PON?,microbial nitrogen?MBN?and water soluble organic nitrogen?WSON?content in the surface soil.No-tillage significantly increased the content of total hydrolysable nitrogen,hydrolysable amino sugar nitrogen,hydrolysable amino acid nitrogen in the 0-10 cm soil layer,increased the content of hydrolysable unidentified nitrogen in the 0-5 cm soil layer.For soil inorganic nitrogen,the content of ammonium nitrate at 0-5 cm and at 5-10 cm under NT was significantly?p<0.05?higher than that of MP,respectively,and the content of ammonium nitrogen in soil at0-5 cm was significantly?p<0.05?higher than that of MP.which was better for increasing the soil nitrogen supply capacity.?2?Soil physical and chemical properties significantly changed after long-term no tillage.No tillage reduced the soil temperature and enhanced the soil moisture.Compared to mouldboard plough,no tillage increased the soil bulk density in plough layer?0-20cm?and soil hardness in surface layer?0-5 cm?,but decreased the soil porosity.No tillage also increased the soil organic carbon,alkali-hydrolysable nitrogen,available phosphorus and available potassium.Soil nitrogen had significant negative correlation with soil temperature,moisture,bulk density and soil hardness.However,soil nitrogen had significant positive correlation with soil porosity,soil organic carbon,alkali-hydrolysable nitrogen and available phosphorus.Soil nitrogen had no relationship with available potassium.?3?The 16S rDNA high-throughput sequencing technology and Real-time PCR technology were used for evaluate the influence of no tillage on the microbial community and nitrogen transformation microbes in black soil.The results showed that tillage only affected the abundance and functional diversity of soil microbial community,but no effect on the microbial community structure.NT increased the diversity of soil microbial community and had higher abundance of bacteria which was involved in nitrogen cycle.The relative abundance of nifH?AOB?AOA in soil nitrogen transformation microbes was higher in no tillage than mouldboard plough.The relative abundance of nosZ was higher in mouldboard plough than no tillage.Soil moisture,pH,organic matter,total carbon and FAD hydrolase was the main factors to affect nitrogen transformation microbes abundance.?4?After long-term no tillage,the nitrogen transformation rate had changed significantly in black soil.NT increased the proportion of MNlab in total mineralization nitrogen and led to the stratification of total mineralization nitrogen among layers.The net mineralization rate of nitrogen in NT was higher than MP due to the lower microbial assimilation rate.NT accelerated the autotrophic nitrification in 0-5cm layer and suppressed the heterotrophic nitrification in all soil layers.In general,long-term NT can provided more effective nitrogen for the growth of corn.Correlation analysis results showed thattotal soil carbon mineralization rate had significant positive correlation with soil organic carbon and total nitrogen.Soil autotrophic nitrogen mineralization rate had significant positive correlation with total soil carbon mineralization rate,soil organic carbon and total nitrogen.?5?The ¹⁵N tracer was applied to study fertilizer utilization rate under no-tillage and mouldboard plough.Results showed that the remaining of ¹⁵N fertilizer had significantly difference between no tillage and mouldboard plough in 0-5cm layer where no tillage was lower than mouldboard plough,but no difference in other layers.The nitrogen fertilizer in the heavy fraction was higher under mouldboard plough than no tillage in all layers.The yield,amount of nitrogen absorbed and ¹⁵N fertilizer absorbed,the utilization rate of fertilizer was significantly higher than mouldboard plough.The distribution of ¹⁵N-labeled nitrogen fertilizer in no-tillage and mouldboard plough was the same in all organs of the plant,in the order of grain>leaf>sheath>stem>bract>panicle,and the grain had the priority in the distribution of ¹⁵N.?6?The static closed chamber-gas chromatography technique was used to collect the N₂O emissions in NT and MP.Results suggested that MP had higher average and cumulative N₂O emissions than NT.The average and cumulative emissions of¹⁵N-N₂O from soil manure under MP were also significantly greater than NT.On average,0.1%-0.16%of the fertilizer nitrogen is lost in the form of N₂O.