| Dissolved organic matter(DOM)is an important active component in soil,and its component content and structural characteristics can sensitively reflect the influence of agricultural activities on farmland soil.Agronomic measures are the key agricultural activities that affect soil physicochemical and biological properties and crop yield,and their impact on soil soluble organic matter is a hot research topic at present.Soil desertification and drought are the key problems affecting agricultural production in the north plateau area of Hebei in recent years.In order to establish the agronomic measures and technical system of cultivating fertility,saving fertilizer and water,increasing yield and increasing efficiency in the north plateau of Hebei,this paper studies three kinds of farming activities in the north plateau of Hebei: planting patterns,amount of organic fertilizer,fertilizer and water management measures.Fluorescence spectrum,ultraviolet spectrum and other techniques were used to analyze the composition characteristics of dissolved organic matter in soil,and the effects of different agronomic measures on the composition characteristics of dissolved organic matter were discussed.By revealing the influence mechanism of dissolved organic matter components,the agronomic technology system on the north plateau of Hebei will optimized.The research results are as follows:(1)Through the study of soil DOM under different planting patterns in the north plateau of Hebei.Visible,In the three-dimensional fluorescence spectra of all types of soil,the peak of fulvic acid(peak A),protein(peak B),humic acid(peak C)and tyrosine(peak D)could be distinguished.The Fex/em values of soil DOM were between 14.83 and 24.29,and the fluorescence peak A was between 17% and21%,the fluorescence peak B was between 5% and 12%,the fluorescence peak C was between 50%and 80%,and the fluorescence peak D was between 6% and 22%.For the comparison of the total fluorescence peak intensity,the greenhouses vegetable field and the open vegetable field were higher than the grassland,while the potato field,silage corn field and oat field were lower than the grassland.In terms of fluorescence peak A,fluorescence peak B and fluorescence peak D,the peak value of oat field was the highest and the peak value of greenhouse vegetable field was the lowest.In terms of fluorescence peak C,the peak value of greenhouses vegetable fields was the highest and that of potato fields was the lowest.Under different planting patterns,the content of DOC in soil ranged from 71.58 to179.64 mg.Kg-1,and the content of DOP in soil ranged from 0.83 to 11.03 mg.Kg-1.overall,in the DOM of farmland soil under high water and fertilizer management in the north plateau of Hebei,the components of humic acid are higher,the degree of humus is higher,and the aromaticity is lower,and they are mainly from the land.DOM in extensive farmland soil has higher content of small molecular components,lower degree of humus and higher aromaticity,and mainly comes from autogenous sources.In order to reduce the loss of soil nutrients in the north plateau of Hebei,cultivate soil fertility,and enhance the ability of soil to resist wind erosion,the planting patterns of organic fertilizer application and high fertilizer and water management should be increase.(2)By studying the effects of different amounts of organic fertilizers on soil DOM components,itcan be known that.With the increase of the amount of organic fertilizer,the soil ∑Fex/em value shows an upward trend,peak A shows A downward trend,peak B shows A parabolic trend,peak C shows an upward trend,and peak D shows A parabolic trend.With the increase of organic fertilizer dosage,the content of DOC and DOP in soil increased.According to fluorescence and ultraviolet spectrum parameters,soil DOM humic acid components presented an upward trend with the increase of organic fertilizer dosage,protein-like components presented an upward and then downward trend,and soil DOM humus degree presented an upward trend.The autobiotics decreased,the terrestrial sources increased,the aromaticity decreased,and the degree of soil deterioration was parabolic.The results showed that excessive application of organic fertilizer increased macromolecular organic matter in soil and decreased soil fertility and microbial activity.The results showed that excessive application of organic fertilizer increased macromolecular organic matter in soil and decreased soil fertility and microbial activity.Therefore,an appropriate amount of organic fertilizer should be applied in the north plateau of Hebei.(3)By studying the effects of different fertilizer and water conditions on soil DOM,it can be seen that with the increase of water,the soil DOM’s ∑Fex/em presents an increasing trend.With the increase of organic fertilizer dosage,the DOM of soil showed a downward trend of ∑Fex/em.Under the carbon-water coupling condition,the DOM of low carbon and high water soil has the highest ∑Fex/em,while the DOM of high carbon and low water soil has the lowest ∑Fex/em.Under the carbon-water coupling condition,the soil DOP and DON contents were the highest in the treatment with high water and high fertilizer,and the lowest in the treatment with low water and low fertilizer.With the extension of culture time,the soil DOM showed A downward trend of ∑Fex/em,the peak of fluorescence peak A showed A downward trend,the peak of fluorescence peak B showed A downward trend,the peak of fluorescence peak C showed A fluctuating change,and the peak of fluorescence peak D showed A downward trend.It shows that soil organic carbon and water are two important factors affecting soil DOM content and components,but their respective mechanisms of action are different.Soil organic carbon is the main source of DOM,and soil moisture is the key factor of soil DOM migration and transformation.Under the combined action of organic carbon and water,DOM in soil is transformed from total organic carbon to DOM,and DOM is transformed from macromolecular components to small molecular components,which are further utilized by biology,and biological residues are then converted into protein-like components of DOM. |
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