Distribution Characteristics Of Iron And Manganese Oxides In Aggregates Of A Paddy Soil With Chinese Milk Vetch Return And Reduced Fertilizer Application

Chinese milk vetch are high-quality organic fertilizer sources for paddy fields in southern China,Chinese milk vetch can bring a large amount of organic materials to the soil and promote the formation of soil aggregates.The frequent alternation of wet and dry conditions in paddy soil will also affect the oxidation of iron and manganese.The form of things.In this paper,rice paddy soils developed by river alluvial deposits(JZ)and river lake sediments(NX)were used as the objects,and the rice-Chinese milk vetch rotation field experiment.The soil aggregates and various forms of iron and manganese oxides(free,amorphous,complex)under Chinese milk vetch returning to the field(returning amount 15,25,30,37.5 t/hm~2)and reduced fertilizer application(20%and 40%).Correlation analysis was used to explore the relationship between aggregates stability and iron-manganese oxide,and path analysis was used to comprehensively evaluate the effect of various forms of iron-manganese oxide on aggregates stability.The field volume is expected to provide a theoretical basis for the rational use of Chinese milk vetch in the double-season rice planting area in the south.The results show that:(1)Compared control,Chinese milk vetch returned increased the content of soil organic matter and available nitrogen.The contents of available phosphorus and available potassium were significantly different between the treatments,which were manifested as application of fertilizer>Chinese milk vetch and application of fertilizer>application of Chinese milk vetch.Among them,when Chinese milk vetch return at 22.5 and 30 t/hm~2,the content of available nitrogen in the soil is increased,while the soil available phosphorus and potassium are supplemented to ensure the balance and supply of soil available nutrients.(2)The distribution of water-stable aggregates with different particle sizes showed that the content of aggregates>5 mm was the highest(28.4～80.8%),followed by 2～0.25 mm,and the lowest content of aggregates was 5～2,0.25～0.053 and<0.053 mm.Compared control,the reduction of chemical fertilizer and Chinese milk vetch increased the content of aggregates>5 mm and reduced the content of aggregates of 2～0.25 and 0.25～0.053 mm after returning.Moreover,the reduction of chemical fertilizer application and the return of Chinese milk vetch to the paddy soil both increased the average weight diameter,geometric average diameter,and water-stable large aggregates of the aggregates,reduced the fractal dimension,and improved the stability of the soil aggregates,but performance trends were different under different amounts of Chinese milk vetch returned to the field.(3)The return of Chinese milk vetch to the field under the application of chemical fertilizers increased the content of amorphous iron and complexed iron and the degree of iron activation of the soil,and had little effect on the content of manganese oxide in the soil.Under reduced fertilization,the content of free iron and manganese in the aggregates decreased,and the content of amorphous and complexed iron and manganese increased significantly with the increase of Chinese milk vetch(15～30t/hm~2).The content of amorphous and complex iron and manganese reached the highest when the fertilizer was40%and Chinese milk vetch was 30 t/hm~2.Compared with treatment of Chinese milk vetch,the content and activation degree of amorphous manganese and complex manganese in two paddy soil aggregates increased after the application of Chinese milk vetch returned to the field with chemical fertilizer,with the decrease of fertilizer application no difference.(4)There is a significant or extremely significant positive correlation between iron oxide and MWD,among which JZ free iron has the best correlation with MWD,and NX complex iron has the best correlation with MWD,the correlation between manganese oxide and MWD in both soils is lower than iron oxide.Path analysis found that iron oxide is an important factor that affects the stability of the agglomerates.The increase of free iron and amorphous iron content in JZ can directly increase the MWD.The amorphous and complex state of iron oxide in the NX.It is a direct factor affecting the stability of the aggregate.