紫云英还田与氮肥减施对水稻土团聚体中各形态铁锰含量的影响

  【目的】  水稻土团聚体的形成和稳定与铁锰氧化物含量密切相关。研究紫云英还田对水稻土团聚体组成以及各粒径团聚体中铁锰形态的影响，以揭示紫云英还田与氮肥减施下土壤团聚体的稳定性机制。  【方法】  田间试验于2015年在湖北荆州进行，供试土壤为长江冲积物发育的水稻土。设置不施氮肥(CK)、紫云英种植还田(MV)、60%氮肥(N_60%)、100%氮肥(N_100%)、紫云英种植还田+60%氮肥(MV+N_60%)、紫云英种植还田+100%氮肥(MV+N_100%) 6个处理。于2019年，采样分析土壤水稳性团聚体百分含量，各粒径团聚体中不同形态的铁锰含量。  【结果】  施肥有效提高了土壤大团聚体(>0.25 mm)含量，以MV+N_60%处理的效果最为明显，比CK处理大团聚体含量增加了49.8%，微团聚体含量减少了71.0%，有效提高了土壤团聚体稳定性。土壤大团聚体中各形态铁锰含量显著高于微团聚体。在>5 mm团聚体中，除游离锰外其余形态的铁锰含量与平均重量直径(MWD)或几何平均直径(GMD)显著相关(r=0.474～0.704)，游离铁和非晶质铁与MWD和GMD均呈极显著正相关。  【结论】  游离铁和非晶质铁是团聚体稳定性的关键因素。紫云英还田与氮肥减施有利于游离铁和非晶质铁在大团聚体中的富集，促进大团聚体的形成，进而改变土壤团聚体粒径分布，提高土壤团聚体的稳定性。

Effects of Chinese milk vetch incorporation and nitrogen reduction on different forms of Fe and Mn in aggregates of paddy soil

  【Objectives】  The formation and stability of soil aggregates are closely related to the content of iron and manganese oxides, which are primarily influenced by management practices and field fertilization. Here, we studied the effect of returning Chinese milk vetch to the field on the aggregate composition and various forms of iron and manganese in paddy soil to reveal the stability mechanism of soil aggregates under nitrogen reduction.  【Methods】  In 2015, a field experiment was conducted in Jingzhou, Hubei Province. The paddy soil derived from Yangtze River alluvial sediment was used as the test material. The treatments in the experiment were CK (no nitrogen fertilizer), MV (Chinese milk vetch planting and returning), N_60% (60% nitrogen fertilizer), N_100% (100% nitrogen fertilizer), MV + N_60% (Chinese milk vetch planting and returning + 60% nitrogen fertilizer), MV + N_100% (Chinese milk vetch planting and returning + 100% nitrogen fertilizer). In 2019, the percentages of soil water-stable aggregates and the contents of various forms of iron and manganese in the aggregates were analyzed.  Rseults  Compared with CK, all fertilization treatments improved the proportion of macroaggregates (>0.25 mm) and soil aggregate stability. The effect of MV+N_60% was highly significant, and increased the content of macroaggregates by 49.8% and decreased the microaggregates by 71.0% compared with CK. The different forms of iron and manganese content in macroaggregates was (P<0.05) higher than in micro-aggregates. Except for free manganese in >5 mm aggregates, the other iron and manganese contents (P<0.05) were correlated with MWD or GMD (r=0.474–0.704). The free iron and amorphous iron showed a highly (P<0.05) positive correlation.  【Conclusions】  Free and amorphous Fe are the key drivers of aggregate stability. Chinese milk vetch incorporation and reduced N input increased the free and amorphous Fe in aggregates, promoted the formation of large aggregates and changed the particle size distribution of soil aggregates which improved soil aggregate stability.