长期施用微肥条件下微量元素和有机官能团在团聚体中的积累特征

Accumulation of Trace Element and Organic Functional Groups in Different Size Fractions of a Loess Topsoil After Long-term Micronutrient Fertilization

微量元素对作物生长至关重要,长期施用微肥可能影响微量元素在农田土壤中的分布,进而影响作物产量及土壤有机碳结构。以渭北旱塬35年锌(Zn)、锰(Mn)、铜(Cu)微肥处理农田为研究对象,分别测定耕层土壤≥250、250~125、125~63、63~20、≤20μm粒级中Zn、Mn、Cu元素含量,并通过傅里叶变换红外光谱(FTIR)测定各粒级有机官能团类型及含量,以期揭示长期微肥下微量元素积累与有机官能团之间的相互关系。结果表明,试验区土壤有机碳含量处于较低水平(6~12 g·kg^(–1)),长期施用Zn、Mn、Cu肥并未显著改善土壤有机碳含量,但导致Zn、Cu元素在表层土壤中明显富集(幅度分别为10%、100%以上),而Mn元素无明显富集(幅度在10%以内)。三种元素在微小团聚体(≤20μm)中的富集程度最高,但该粒级有机碳抗分解能力最小(0.30~0.32),这主要因为该粒级不稳定官能团C-O含量较高且矿物含量较高,与有机碳稳定性正相关的C=O、C=N、C=C含量少。试验区土壤中Cu元素积累与C-O、C=O、C=N呈正相关,而Zn、Mn元素与官能团之间无相关性,这与有机碳丰富的土壤存在较大差异。综上,长期施用微肥未显著改变试验区表层土壤有机碳含量及结构,但导致Zn、Mn、Cu元素在表层微小团聚体中产生不同程度的积累,这主要与有机碳总量、有机官能团含量及类型、元素吸附效率有关。

【Objective】Trace elements are of vital importance in crop growth.Long-term application of micronutrient fertilizers may affect the distribution of the elements in farmland soil,therefore influencing crop yield and soil organic carbon composition.To explore the accumulations of trace elements in different size fractions of loess soil,we collected topsoils from field plots after 35 years of fertilization with Zn,Mn,and Cu.【Method】All the soil samples from the treated plots and control plots(CK)were fractionated into≥250,250-125,125-63,63-20,and≤20μm.The element contents,availability,and soil organic carbon content(SOC)were determined and compared.Also,the types and contents of organic functional groups in different size classes were determined using Fourier Transform Infrared(FTIR)spectrometer.【Result】The results show that the content of SOC in the treated plots was at a low level(6-12 g·kg^(–1))and was not significantly improved after applying Zn,Mn,and Cu fertilizers.Nevertheless,the three trace elements were enriched to different degrees:Zn and Cu fertilizers significantly increased the total contents of Zn and Cu(the degree of enrichment was above 10%and 100%respectively),but no evident Mn enrichment was observed under Mn fertilizer treatment(the degree of Mn was within 10%).The highest concentrations of Zn,Cu,and Mn were observed in the≤20μm fractions,but SOC stability in this fraction was the lowest,ranging between 0.30-0.32.This was mainly because of the greater content of the unstable functional group C-O,but lower contents of C=O,C=N,and C=C that were positively correlated with the recalcitrance of SOC.The functional groups(C-O,C=O,C=N)were positively associated with the accumulation of Cu in the soil.Also,the inconsistent relationships of Zn,Mn,and functional groups observed in the loess soil in this study suggest that the governing principals in this study were distinct from previous reports based on SOC-rich soils.【Conclusion】Findings in this study suggest that long-term application of micronutrient fertilizers did not significantly change the content of organic carbon or organic carbon composition in the topsoil of our study area.Nevertheless,it enhanced the accumulation of Zn,Mn,and Cu in the micro-aggregates to varying degrees.This is affected by the total organic carbon,the content of organic functional groups,and the type and efficiency of elements adsorption together.