Effect Of Nitrogenous Fertilizer And Biochar On Sugarcane Growth And Soil Ammonia Oxidation

The common continuous cropping or perennial cultivation methods and Long-term excessive addition of nitrogen fertilizer in sugarcane farm leads to low nitrogen fertilizer utilization,and a large number of active nitrogen losses have also caused a series of ecological and environmental problems.In recent years,application of biochar plays a vital role in the process of soil improvement,nitrogen conversion and utilization regulation.In addition,Ammonia oxidation is a crucial process for soil nitrogen transformation and plays an essential role in controlling nitrogen loss in farmland and improving nitrogen use efficiency.Understanding the response of ammonia-oxidizing archaea?AOA?and ammonia-oxidizing bacteria?AOB?to environmental changes may help to improve agricultural soil nitrogen management strategies.This thesis studied the effects of nitrogen fertilizer and biochar application on the fundamental biological processes of nitrogen transformation in sugarcane continuous cropping soil.The sugarcane continuous cropping soil with more than 20years of cultivation and the main planting variety ROC22 in China's sugarcane area is the research object.Through pot and field trials,two nitrogen application levels(0 and 310.5 kg/hm² pure nitrogen,N_0¹)were added to treat different biochar quantities(7.5×10³².4×10⁴ kg/hm²,record B_1²),no biochar was applied to the control under each nitrogen application rate(record N_0¹B₀).The effects of nitrogen fertilizer and biochar on soil pH,nitrogen form transformation,nitrification potential,ammoxidation,microbial abundance and community composition were discussed.The biological characteristics of potted sugarcane seedlings to the elongation stage and the yield of sugarcane process in the field were studied.The traits were analyzed.The results show:1)Compared with single biochar N₀B₁ or single nitrogen application N₁B₀ treatment,nitrogen application and biochar?N+B?treatment have better growth promoting effect and yield increasing effect on sugarcane seedling growth and sugarcane yield traits.Compared with N₁B₀ treatment,N₁B_1² treatment increased the sugarcane biomass by 10.82%and 6.05%,respectively?P<0.05,P>0.05?,and N₁B₁ treatment increased the sugarcane stem weight by 18.52%?P>0.05?.Compared with N₀B₀treatment,N₀B₁ treatment had no significant effect on the growth of sugarcane seedling stage to maturity stage?P>0.05?;N₁B₀ treatment significantly promoted the growth of sugarcane seedling stage-extension root,stem,leaf and elongation-mature sugarcane stem?P<0.05?.2)Soil physical and chemical results show that the biochar treatment can increase the soil pH value regardless of nitrogen application.The soil pH of the tested soil under the pot experiment and field test conditions is increased by 0.22⁰.51 and 0.02⁰.11 units respectively.Nitrogen fertilizer or biochar treatment had significant effects on soluble nitrogen and its composition?P<0.05?,but had no significant effect on total nitrogen TN content in the root zone?P>0.05?.In the pot experiment,compared with N₁B₀ treatment,soil soluble total nitrogen TSN and nitrate nitrogen NO₃^--N content in N₁B₁ treatment decreased significantly?P<0.05?but increased significantly under N₁B₂ treatment?P<0.05?.In the field experiment,compared with N₀B₀ treatment,N₁B₀ treatment significantly increased the soil TSN content in the root zone by12.05¹4.92 times?P<0.01?within 1⁴ weeks of top dressing,and the ratioofNH₄⁺-NandNO₃^--Nwas96.32%⁷0.10%and2.71%²7.91%;After 2³ months of top dressing,the TSN content in the root zone was still 1.81².95 times higher than that of the control?P<0.05?,but the proportion of NH₄⁺-N and NO₃^--N changed to31.78%⁵6.63%and 66.87%¹5.19%.In addition,compared with N₁B₀,N₁B₁ treatment significantly increased the accumulation of TSN and NO₃^--N in the root zone during the period from 8 days to 96 days.3)Nitrification potential results showed that in the pot experiment,compared with N₁B₀ treatment,the soil nitrification potential level in root zone decreased significantly under N₁B₁ treatment?P<0.05?,but increased significantly under N₁B₂ treatment?P<0.05?.This indicates that under the premise of nitrogen application,the different addition ratio of biochar has the potential to regulate soil nitrification potential.In the field experiment,compared with N₁B₀ treatment,N+B treatment reduced the nitrification potential from 8 days to 28 days in the early stage of nitrogen application and increased the nitrification potential from 75 days to 96days in the middle and late stages of nitrogen application.This phenomenon of peak-shaving is one of the crucial reasons for improving soil nitrogen retention and promoting sugarcane growth.The results of pot experiment and field experiment showed that there was a positive correlation between soil nitrification potential and NH₄⁺-N content without nitrogen application?r=0.494,r=0.523,P>0.05,P<0.01?.There was a significant positive correlation between soil nitrification potential NP and TSN and NO₃^--N content?P<0.05?.4)The results of real-time PCR analysis showed that the AOA abundance in the root zone was much higher than that in the AOB abundance without nitrogen application.In the nitrogen treatment,the AOB abundance in the root zone was significantly increased while the AOA abundance was significantly reduced?P<0.05?.The high-throughput sequencing results of Illumina Miseq showed that the dominant community of ammonia-oxidizing bacteria in the soil of sugarcane roots was Nitrosospira,and the nitrogen application significantly reduced its abundance by 29.05%?P<0.05?.The dominant community of ammonia-oxidizing archaea was mainly Nitrososphaera,and the single biochar treatment significantly increased its abundance by10.15¹3.46 times?P<0.01?.Correlation analysis showed that soil pH,soluble organic carbon and total soluble nitrogen might be the main environmental factors affecting the composition of AOB and AOA communities.Compared with the single nitrogen application treatment,N+B treatment resulted in changes in the abundance,community composition and AOA/AOB niche of AOB and AOA,which may have important control effects on soil nitrogen loss process.Based on the above results,nitrogen fertilizer should be applied moderately in the process of sugarcane cultivation,and an appropriate amount of biochar should be applied to improve the supply of available nitrogen in the root zone and promote the directional transformation and efficient utilization of soil nitrogen in continuous cropping of a sugarcane field.