摘要
[目的]探究长期不同施氮量对土壤团聚体碳氮含量及小麦产量的影响,为合理施氮提供理论依据.[方法]基于设置在河南省许昌市张潘镇 4 个不同施氮水平 11 年定位试验,施氮量分别为 0(N0)、180 kg·hm-2(N1)、240 kg·hm-2(N2)及 300 kg·hm-2(N3),分析不同处理土壤碳氮含量、团聚体分布及其碳氮含量的变化,并探寻长期施氮对小麦产量及其构成的调控路径.[结果]随着施氮量增加,各土层土壤团聚体分布呈现大团聚体(＞0.25 mm)向微团聚体(0.053-0.25 mm)和粉黏粒组分(＜0.053 mm)转化的趋势,显著降低了团聚体平均重量直径(MWD).土壤碳、氮含量在 0-20 cm土层随施氮量增加而逐渐上升,20-40 cm土层呈先升高后降低趋势.与N0 相比,0-20 cm土层各施氮处理土壤有机碳和全氮含量的平均增幅分别为 13.1%—37.2%和 19.4%—29.4%;20-40 cm 土层的平均增幅分别为 15.3%—32.2%和6.1%—29.3%.长期施氮处理显著提高了各粒级团聚体有机碳含量,与 N0 相比,施氮处理大团聚体有机碳平均含量提高 31.6%—62.0%,微团聚体提高 8.7%—61.2%,粉黏粒提高 14.0%—81.7%.在 0-20 cm土层,各粒级团聚体全氮含量亦随施氮量增加而增加,各施氮处理大团聚体、微团聚体和粉黏粒中全氮含量平均增幅分别为 32.6%—51.0%、25.7%—35.9%和 3.2%—9.7%,且均以N3 处理最高.在 20-40 cm土层,各粒级团聚体全氮含量随施氮量增加呈先升高后降低趋势,各施氮处理大团聚体、微团聚体和粉黏粒全氮含量平均增幅分别为 17.6%—35.2%、11.7%—24.0%和 1.1%—12.9%,且均以N1 处理最高.研究结果还表明,长期施氮显著增加了小麦成穗数和穗粒数,进而提高了产量.与N0 相比,N1、N2 和N3 处理分别提高小麦产量 188.1%、177.3%和 173.2%.相关分析与结构方程模型分析表明,小麦产量与土壤碳、氮含量及团聚体中碳、氮含量均呈显著正相关,长期施氮通过改变土壤及团聚体中碳、氮含量进而影响小麦产量.[结论]综上,长期合理施氮提高了土壤及团聚体中碳、氮含量,提升了土壤肥力,促进小麦增产.在本试验条件下以施氮量 180 kg·hm-2 时最优.
Abstract
[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.
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