Difference In Nitrogen Responses And Nitrogen Efficiency Of Paddy Soils In Southern And Northern China Under The Same Climatic Condition

Currently,there are significant differences in nitrogen responses,uptake and utilizition in rice of paddy fields between southern and northern China.Most previous research focused on different spatial scales and fail to discount the effects of climate,soil and variety,making it difficult to distinguish the contribution of soil in this.To address this issue,the pot experiment with ¹⁵N tracing was conducted in Harbin,Heilongjiang Province,in 2018 and 2019.The experimental soils were black paddy soil collected from Heilongjiang,gleyed paddy soil collected from Jiangsu and red paddy soil collected from Hunan.Three N fertilization levels were established for each soil:No nitrogen application（N0）,0.87 g N·pot^-1(N1,equivalent to 150 kg·N·hm^-2)and 1.74 g N·pot^-1(N2,equivalent to 300 kg N·hm^-2).Tiller number,SPAD value,rice yield,dry weight,earing rate were determined as well as nitrogen utilization efficiency,nitrogen content and nitrogen mineralization amount of three soils.In this study,the effects of soil and nitrogen amount on rice growth and nitrogen efficiency were investigated.The difference in nitrogen response and nitrogen efficiency of paddy fields between northern and southern China were clarified to provide a reference for regulating regional differences in nitrogen efficiency.The main experimental results are as follows.（1）There was a notable difference in initial inorganic nitrogen content and cumulative mineralized nitrogen of different soils.initial inorganic nitrogen content was in descending order:red paddy soil,black paddy soil,gleyed paddy soil.Initial inorganic nitrogen content of red paddy soil was significantly 17.95%and 10.99%than black paddy soil and gleyed paddy soil,respectively.Water-logged incubation over 28 days showed that cumulative mineralized nitrogen of red paddy soil was 98.53%-381.69%than others.Gleyed paddy soil and red paddy soil’s nitrogen mineralization rate increased firstly and then decreased,while the black paddy soil had the smoothest nitrogen supply process.（2）Nitrogen application significantly increased the SPAD of rice leaves and also significantly promoted the uptake of nitrogen by grain and straw.Nitrogen accumulation was higher in red paddy soil than in the others,and rice leaf SPAD of ed paddy soil was highest in the N0 treatment.The differences in plant nitrogen content and nitrogen accumulation were not sig nificant between gleyed paddy soil and black paddy soil,and plant nitrogen content and nitrogen accumulation of black paddy soil were 31.03%and 43.78%higher than others.（3）Soil types had significant effects on tiller numbers and earing rate.Nitrogen application significantly affect that in elongation stage and maturity stage.Compared with N0 treatment,tillers number of red paddy soil increased by 56.64%-77.61%,which of greyed paddy soil increased by21.90%-38.40%.Without nitrogen application,rice tiller numbers on red paddy soil was 26.33%higher than that on black paddy soil,and 40.65%higher than that on gleyed paddy soil.Nitrogen had a remarkable influence on spike rate in 2018,with the N2 treatment higher than the N0treatment by 26.17%,while nitrogen no significant effect on spike rate in 2019.Soil type had a significant effect on on tiller numbers in 2018,while there was no effect in 2019.（4）Soil type and nitrogen application remarkably contribute to Ndff(the percentage of nitrogen drived from ¹⁵N fertilizer).In the first growth season（2018）,black paddy soil absorb10.51%and 22.20%more nitrogen fertilizer than gleyed paddy soil and red paddy soil respectively.The difference in soils was smaller in the next season.nitrogen appli cation also remarkably contribute to Ndff,which of N2 treatment was 46.21%higher than that of N1 treatment.Besides,The Ndff of soils in 2019 was 26.35%significant lower than that in 2018.The fate of fertilizer ¹⁵N varied among soils,with the first season ¹⁵N being mainly absorbed in black paddy soil（31.4%-41.31%）,residues and losses in greded paddy soil（32.19%-41.17%）,and residues in red paddy soil（32.46%-41.14%）.In 2019,a smaller proportion of the second season ¹⁵N was absorbed（3.05%-5.72%）,while ¹⁵N was mainly residual or lost through other ways.（5）Soil types had a significant influence on rice yield.Rice yield on red paddy soil without nitrogen application remarkably higher than greyed paddy soil and black paddy soil,at 90.90%and53.64%.Compared with greyed paddy soil and black paddy soil,AE_N（nitrogen agronomic efficiency）,PFP_N（partial factor productivity of applied N）and RE_N（nitrogen recovery efficiency）are all lower in red paddy soil.The AE_N（Nitrogen agronomic efficiency）of black paddy soil was25.68%higher than gleyed paddy soil,while the PFP_N（partial factor productivity of applied N）of gleyed paddy soil was 4.72%higher than black paddy soil.Nitrogen application increased yields by 93.41%and 43.88%in black paddy soil and gleyed paddy soil,while the yield of red paddy soil was not benefit a lot from nitrogen application.