减施化肥下紫云英翻压量对土壤团聚体及铁锰氧化物的影响

Effects of different returning amount of Chinese milk vetch on soil aggregates and iron and manganese oxides under reduced fertilizer application

以湖南省南县长期紫云英-双季稻轮作的土壤为对象,在化肥减量20%和40%,紫云英翻压量15、22.5、30、37.5 t·hm^(-2) 4个水平下,研究减量化肥与翻压不同量紫云英的土壤团聚体中铁锰氧化物的变化及与团聚体水稳性的关系。结果表明:(1)与对照[紫云英翻压(MV)和施用100%化肥(F)处理]相比,减施20%和40%化肥配施紫云英增加了>0.25 mm团聚体的含量,降低了<0.25 mm团聚体的含量;减施化肥下紫云英翻压量在15和22.5 t·hm^(-2)时团聚体稳定性提高8.91%~45.45%。(2)与对照相比,减施化肥20%紫云英翻压量为15~30 t·hm^(-2)时,土壤团聚体的游离铁锰含量随着翻压量的增加呈现下降的趋势,但非晶质、络合铁锰含量分别显著提高7.70%~72.31%和10.75%~58.53%。(3)相关性与通径分析显示,化肥减施与紫云英翻压下土壤团聚体稳定性主要取决于铁氧化物的含量;而在铁氧化物中,非晶质与络合态铁对团聚体稳定性的提高起直接作用。

The soils of long-term Chinese milk vetch-double cropping rice rotation in Nanxian County,Hunan Province were taken as the research object.When the fertilizer reduction was 20%and 40%,and the return amount of Chinese milk vetch was set at 15,22.5,30,37.5 t·hm-2,the effects of both reduced fertilizer and different returning amount of Chinese milk vetch on iron-manganese oxides in soil aggregates and their relationships with water stability of aggregates were studied.The results showed that:(1)Compared with the control[alone returning of Chinese milk vetch(MV)and application of 100%fertilizer(F)],reducing the application of 20%and 40%of the chemical fertilizers combined with the application of Chinese milk vetch increased the content of>0.25 mm aggregates,reduced the content of<0.25 mm aggregates;the stability of aggregates increased by 8.91%~45.45%at 15 and 22.5 t·hm-2 Chinese milk vetch returning when reduced the application of chemical fertilizers.(2)Compared with the control,when the fertilizer was reduced by 20%,the free iron and manganese content in the soil aggregates decreased with the increase of returning amount of Chinese milk vetch(15~30 t·hm-2).But the content of crystalline and complex iron and manganese significantly increased by 7.70%~72.31%and 10.75%~58.53%,respectively.(3)Correlation and path analysis showed that the stability of soil aggregates under chemical fertilizer reduction and Chinese milk vetch returning mainly depended on the iron oxide contents.While in iron oxides,amorphous and complex irons played a direct role in improving the stability of aggregates.