长期施肥对棕壤铁形态及其有效性的影响

【目的】利用沈阳农业大学棕壤肥料长期定位试验，研究不同施肥处理对耕层土壤酸碱度（pH）、氧化还原电位（Eh）和有机质的影响，探讨不同施肥条件下土壤游离态氧化铁、无定形氧化铁、亚铁总量和有效铁含量的变化以及与pH、Eh和有机质的关系。 【方法】本文选取试验处理为CK（不施肥）、N（氮肥）、NP（氮磷肥配施）、NPK（氮磷钾肥配施）、M（有机肥）、MN（有机肥与氮肥配施）、MNP（有机肥与氮磷肥配施）、MNPK（有机肥与氮磷钾肥配施）。在2014年大豆收获期，采集了不同施肥处理0-20 cm耕层土壤样品，分析了土壤pH、Eh、有机质含量以及游离态氧化铁、无定形氧化铁、亚铁和有效铁含量。 【结果】与1979年原始土壤相比，所有处理土壤pH显著降低了0.6~1.4个单位。不施肥处理土壤有机质下降了11.5%，化肥处理有机质略有下降，而有机肥处理有机质含量显著增加。所有处理有效铁含量显著增加，化肥有机肥配施增加幅度更大；与2014年不施肥处理相比，施用氮肥处理土壤pH最低，而氮肥配施磷、钾和有机肥中的一种或几种pH又有所上升，其中配施有机肥效果最明显；施用化肥处理土壤Eh增加，而施用有机肥处理Eh则下降。施用化肥土壤游离态氧化铁和有效铁含量增加，亚铁含量下降，而施用有机肥土壤游离态氧化铁降低，亚铁总量及有效铁含量增加。 【结论】经过长期耕作和施肥，土壤pH显著下降，有效铁含量显著增加。长期不施肥土壤有机质显著下降。施用氮肥土壤酸化趋势明显，磷、钾和有机肥配施能够缓解氮肥引起的酸化现象。施用有机肥显著降低土壤氧化还原电位，有利于氧化态铁向还原态铁转化，更有利于增加土壤有效性铁的含量。

Effects of long-term fertilization on iron fraction and availability in brown soil

Objectives] The study was designed to explore the influences of long-term fertilization on soil pH,Eh,and organic matter based on the long-term fertilization experiment in Shenyang Agricultural University.The study also aimed to investigate variations of free iron oxide,amorphous iron oxide,total ferrous iron,and available iron in soil under different fertilizer treatments,and to find the relationships between different iron fractions and pH,Eh and organic matter.Methods] The treatments selected in the experiment were CK (no fertilizer),N (nitrogen fertilizer),NP (nitrogen + phosphorus fertilizers),NPK (nitrogen + phosphorus + potassium fertilizers),M (organic fertilizer),MN (organic fertilizer + nitrogen fertilizer),MNP (organic fertilizer + nitrogen + phosphorus fertilizers) and MNPK (organic fertilizer + nitrogen + phosphorus + potassium fertilizers).Soil samples were collected from 0-20 cm top soil in different fertilization plots at the harvest of soybean in 2014.We determined soil pH,Eh,and organic matter,and the contents of free iron oxide,amorphous iron oxide,total ferrous iron,and available iron in these samples.Results] Compared to that in original soil in 1979,the present soil pH values for all treatments were significantly decreased by 0.6-1.4 units.The contents of soil organic matter were decreased by 11.5％ in the no fertilizer treatment (CK),slightly decreased in the chemical fertilizer treatments,and significantly increased in the organic fertilizer treatments.The contents of available Fe for all treatments were markedly increased,and most notably for the chemical and organic fertilizers co-used treatments.Compared to that in the CK in 2014,the soil pH was the lowest in the N fertilizer treatment,but raised again when the P,K and/or organic fertilizers were co-used,and most notably when the organic fertilizer was used in soil.The soil Eh values were increased in the chemical fertilizer treatments,while the values were decreased in the organic fertilizer treatments.The contents of free iron oxide and available iron were increased and the contents of total ferrous iron were decreased in the chemical fertilizer treatments.The contents of free iron oxide were decreased and the contents of total ferrous iron and available iron were increased in the organic fertilizer treatments.Conclusions] The long-term fertilization can cause a significant decrease of soil pH and significant increase of available iron.The long-term no fertilization can cause a significant decrease of soil organic matter content.The use of single N fertilizers will lead to vital decline of soil pH,but will not when combined with the phosphorus,potassium and/or organic fertilizers.The use of organic fertilizers will induce the decrease of soil Eh,benefit the transformation of oxide iron to ferrous iron,which is further helpful for the increase of soil available iron.