Effects of Different Nitrogen Application Rates on Carbon and Nitrogen Content of Soil Aggregates and Wheat Yield
[Objective]The influence mechanism of varying nitrogen(N)rates on the carbon(C)and N content of soil aggregate,as well as wheat yield were investigated in this study,so as to provide a scientific basis for the rational application of N fertilizer.[Method]The 11-year experiment was conducted in Zhangpan Town,Xuchang City,Henan Province,with four different N levels,including 0(N0),180 kg·hm-2(N1),240 kg·hm-2(N2),and 300 kg·hm-2(N3).The study systematically analyzed changes in soil carbon and nitrogen content,cluster distribution and their carbon and nitrogen content in different soil layers as a result of long-term N application,and investigated the regulatory pathways of long-term N application on wheat yield and its composition.[Result]There was a transformation in the composition of soil aggregates in every soil layer,specifically from larger macroaggregates(＞0.25 mm)to microaggregates(0.25-0.053 mm)and silt and clay particles(＜0.053 mm),as well as an increase in N rate.Additionally,the application of N resulted in a significant decrease in the mean weight diameter(MWD).As N application rates increase,the C and N content of the soil increased in the 0-20 cm layer,the C and N content of the soil in the 20-40 cm soil layer showed the trend to increase at first and then decrease.Compared with the N0 treatment,N application increased soil organic carbon(SOC)and soil total nitrogen(STN)content by 13.1%-37.2%and 19.4%-29.4%in the 0-20 cm layer and by 15.3%-32.2%and 6.1%-29.3%in the 20-40 cm layer,respectively.The N treatment significantly increased the SOC content of each particle size aggregates compared with N0 treatment,with the SOC content of macroaggregates increasing by 31.6%-62.0%,the SOC content of microaggregates increasing by 8.7%-61.2%and the SOC content of silt and clay increasing by 14.0%-81.7%.As N application rates increased,the STN content of the soil increased in the 0-20 cm layer.With the STN content of macroaggregates increasing by 32.6%-51.0%,the STN content of microaggregates increased by 25.7%-35.9%and the STN content of silt and clay increased by 3.2%-9.7%,the N3 treatment had the highest STN content of all particle size aggregates.In the 20-40 cm soil layer,the STN content of all particle size aggregates tended to increase at first and then decrease.With the STN content of macroaggregates increasing by 17.6%-35.2%,the STN content of microaggregates increased by 11.7%-24.0%and the STN content of silt and clay increased by 1.1%-12.9%,and the N1 treatment had the highest STN content of all particle size aggregates.The study results indicated that long-term nitrogen application had a significant impact on the spike number and grain number per spike in wheat,resulting in increased yield.Compared with the N0 treatment,the application of N1,N2,and N3 treatments resulted in a significant increase in wheat yield,with improvements of 188.1%,177.3%,and 173.2%,respectively.The correlation and structural equation modelling analyses revealed a significant and positive correlation between wheat yield and soil carbon and nitrogen content,as well as carbon and nitrogen content in aggregates.Additionally,the long-term application of nitrogen was found to influence wheat yield formation by affecting carbon and nitrogen content in microaggregates.[Conclusion]In summary,the application of nitrogen over a long period of time raised the content of carbon and nitrogen in both soil and aggregates,enhanced soil fertility,ultimately promoting wheat yield.The optimal nitrogen application rate was 180 kg·hm-2 under the condition of this experiment.
nitrogen application ratessoil aggregatescontent of carbon and nitrogenwheat yield
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