| Soil organic carbon（SOC）is the core material of soil nutrient cycle and supply.Improving SOC retention is helpful to enhance soil structure stability and agricultural productivity,and plays an important role in soil quality and agricultural sustainable development.Exogenous organic materials are the main application source of soil organic carbon and the key to affect the content and stability of SOC.Due to the different chemical properties of different organic materials,the application into the soil will lead to different decomposition process,decomposition and transformation rate,resulting in differences in the distribution of SOC and components;In addition,50%～75%of SOC in farmland soil can combine with soil clay particles to form a stable organic-inorganic complex.In the binding mechanism between soil organic carbon and minerals,metal cations play an important role.They can be used as a bond bridge between organic carbon and mineral particles,so as to improve the stability of soil organic carbon.The trace metal element zinc is an essential micronutrient for plants,and zinc fertilizer is a common trace element fertilizer in farmland.So far,there have been many studies on the application of organic materials and the effectiveness of SOC on zinc,but there are few studies on the influence and mechanism of zinc on SOC turnover and stability.Therefore,through a 60 day indoor culture experiment,this study aims to reveal the effects and mechanisms of zinc combined with different organic materials on soil aggregate formation and soil organic carbon turnover.The main results of the study are as follows:（1）The content distribution of SOC,POC and MAOC under single application of Zn fertilizer,different organic materials,and coordination between Zn and organic materials were comparatively analyzed.The results showed that the addition of an equal carbon amount of wheat straw and humified sheep manure could significantly increase the SOC content,which increased by 4.62%,21.65%（P<0.05）,respectively,in soils supplemented with wheat straw and humified sheep manure up to 30 d of culture;When cultured to 60 d,they increased by 7.22%,29.51%,respectively（P<0.05）.It can be seen that the addition of humified sheep manure increased the SOC content by a much higher extent than the wheat straw,while the application of Zn had no significant effect on the SOC content.The POC content of the two stages 0-30 d and 0-60 d with Zn application was increased by22.21%,18.9%,respectively,compared with that without Zn application（P<0.05）;The POC content was significantly increased by 14.35%by the addition of straw during 0-60d compared with no addition;The addition of humified sheep manure increased POC content by 40.71%,9.66%at the two stages of 0-30 d and 0-60 d,respectively,compared with no addition.There were no significant differences in soil MAOC contents between Zn-applied and no Zn-applied soils from 0-30 d,whereas for the whole cultivation period,soil MAOC contents decreased by 5.66%（P<0.01）under Zn-applied conditions;The addition of wheat straw and humified sheep manure significantly increased the soil MAOC content throughout the incubation period,which was 3.65%,21.73%higher than that without organic materials during 0-30 d,and 4.36%,19.63%higher than that at the end of incubation,respectively.It can be seen that the effect of adding humified sheep manure to increase the MAOC content was much higher than that of wheat straw.（2）The soil water stable aggregate formation,stability and its SOC content distribution were comparatively analyzed.The results showed that the content of micro aggregates and clay particles decreased by 8.17%,22.41%and the content of fine and large aggregates increased by 27.35%during the period from 0-60 d with Zn application,which indicated that Zn application promoted the aggregation of small aggregates to fine and large aggregates;The addition of different organic materials enhanced soil aggregate formation throughout the culture period,and the addition of wheat straw during 0-30d decreased micro-aggregates,mucilage-aggregates by 10.35%,26.71%,and macro aggregates by 26.6%,respectively,compared with no addition;During 0-60 d,the viscomate pellet content decreased by 23.77%,while the coarse aggregates,fine and large aggregates increased by 32.12%,15.70%,respectively,and it was additionally found that by the end of the incubation period,its macro-aggregate content was significantly decreased by 6.64%compared to that during 0-30 d.This indicated that the large aggregates formed by the addition of wheat straw readily disintegrated and broken over time in culture;The addition of humified sheep manure decreased the mucus pellet content by 19.83%and the fine and large agglomerates content by 20.48%during 0-30 d;However,the content of micro-aggregates and myxo-aggregates decreased by 5.67%and 16.16%during 0-60 d,while the content of coarse and fine macro-aggregates increased by 46.10%and 10.51%,respectively,and the content and stability of ma cro-aggregates formed increased significantly.From these,it can be concluded that the main factor affecting aggregate formation is not the amount of C input,but related to the chemical composition of the organic material.Zn application significantly decreased the small aggregate SOC content while increasing the large aggregate SOC content during 0-60 d;The addition of humified sheep manure during the whole incubation period increased aggregate SOC content at each particle size more than wheat straw.（3）By analyzing the content of total Zn and various forms of Zn in original soil and aggregates.The results showed that the content of total Zn in native soil,POM and MAOM under Zn application was 102～108 mg·kg-1,73～97 mg·kg-1 and 100～105 mg·kg-1respectively,which was 30.75%,43%and 30%higher than that without Zn application;The content range of wheat straw treatment was 77～79 mg·kg-1,52～60 mg·kg-1 and 78～79 mg·kg-1 respectively,which had no significant change compared with the control;After adding rotten sheep manure,the contents of total Zn in original soil,POM and MAOM were 81～82mg·kg-1,73～75 mg·kg-1 and 82～83 mg·kg-1 respectively,which were increased by 3.58%,45.32%and 6.88%respectively compared with the control.Obviou sly,the addition of Zn and rotten sheep manure can improve the content of total Zn in soil more than wheat straw.The contents of soil exchangeable Zn（Ex-Zn）,loose organic Zn（Lom-Zn）and carbonate bound Zn（Carb-Zn）increased by 7.37%,3.66 and 2 times respectively;The content of Lom-Zn increased by 28.86%and the content of Carb-Zn decreased by 11.96%during 0-60 d;The content of Lom-Zn increased by 1.6 times and the content of Carb-Zn decreased by 27.11%during 0-30 d,while the contents of Ex-Zn,Lom-Zn and Carb-Zn increased by 4.18%,1.3 times and 20.52%respectively during 0-60 d.It can be seen that the addition of rotten sheep manure can affect the content distribution of total Zn and various forms of Zn more than wheat straw.In conclusion,Zn application can increase the relatively active organic carbon component,but reduce the stable organic carbon component.The addition of rotten sheep manure is more conducive to the increase of SOC content than crop straw,straw is more conducive to the increase of active carbon content,and rotten sheep manure is more conducive to the increase of stable organic carbon content;Zn application could significantly promote the formation and stability of soil aggregates.The formation of soil aggregates was faster but its stability was poor under the condition of adding crop straw,while the formation of soil aggregates was slower but more stable under the condition of adding rotten sheep manure;Both organic materials can increase the content of Lom-Zn in soil.This shows that the reasonable combination of zinc fertilizer and organic materials can promote the improvement of soil structure,but it is not conducive to the maintenance of soil organic carbon stability. |
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