长期不同施肥对土壤溶解性有机质含量及其结构特征的影响

以长期定位试验为研究平台，并结合紫外-可见吸收光谱，探求长期不同施肥管理措施：(1)CK(不施肥)；(2)NPK(氮磷钾)；(3) NPKS(化肥+稻草还田)；(4)1.5NPKS(1.5倍化肥+稻草还田)；(5)NPKM(化肥+猪粪)下0～20，20～40和40～60 cm土层的溶解性有机质(DOM)含量和结构特征。结果表明，长期施用化肥对土壤DOM的影响较小，化肥配施秸秆NPKS和化肥配施有机肥NPKM均显著提高了耕层土壤DOM的含量，在0～20 cm耕层土层DOM含量比化肥NPK处理分别提高39.1和12.1 mg·kg-1。相比不施肥和氮磷钾处理，化肥配施秸秆或配施有机肥明显降低0～20和20～40 cm土层溶解性有机质碳与有机氮的比值，提高了土壤供氮能力。长期施肥对40～60 cm土层DOM含量和溶解性有机质碳氮比没有明显影响，不同处理间差异不显著。在0～20和20～40 cm土层，相对于不施肥和氮磷钾处理，NPKM，NPKS和1.5NPKS处理能提高土壤DOM的共轭结构和腐殖化程度；在40～60 cm土层，提升效果不明显。化肥配施秸秆或有机肥能增加0～20 cm土层的紫外光谱吸收值(SUVA₂₅₄，SUVA₂₆₀和SUVA₂₈₀)和吸收系数α(355)，降低吸光度比值(A₂₅₀/A₃₆₅)，表明0～20 cm土层DOM的芳香度、疏水性、分子量和CDOM含量增加，在20～40和40～60 cm表现不明显。不同土层的A₃₀₀/A₄₀₀值均大于3.5，表明土壤中主要以富里酸为主。综上，长期化肥配施秸秆或配施有机肥能够提高0～20和20～40 cm土壤溶解性有机质的含量，降低溶解性有机质碳氮比，提升土壤肥力；同时增加0～20 cm土壤DOM共轭结构、腐殖化程度、芳香度、疏水部分比例和平均分子量。长期施肥对40～60 cm土层DOM含量和结构影响较小。

Effect on Soil DOM Content and Structure Characteristics in Different Soil Layers by Long-Term Fertilizations

National Monitoring Station of Soil Fertility as a research platform was used combined with UV-Visible absorption spectroscopy to explore how the following fertilizer application: (1) CK (non-fertilization); (2)NPK (applied chemical nitrogen, phosphorus and potassium); (3) NPKS (chemical nitrogen, phosphorus and potassium combined with straw); (4) 1.5NPKS (1.5 times of chemical nitrogen, phosphorus and potassium combined with straw); (5) NPKM (chemical nitrogen, phosphorus and potassium combined with manure) to influence the DOM content and structure in 0~20 and 20~40 and 40~60 cm soil layers. The results showed that long term application chemical fertilizers had less effects on soil DOM content, but chemical fertilizers combined with straw and organic manure significantly increased soil DOM content by 39.1 and 12.1 mg·kg-1 in topsoil. Compared to CK treatment and NPK treatment, chemical fertilizers combined with manure and straw could decrease C/N in 0~20 and 20~40 cm soil layers, and improved the supply of nitrogen in soil, but the DOM and C/N had not significantly difference between different fertilizations in 40~60 cm soil layer. In 0~20 and 20~40 cm soil layers, compared to CK treatment and NPK treatment, the treatments of NPKM，NPKS and 1.5 NPKS increased conjugated structure and humus of soil DOM . In 40~60 cm soil layer, the increased by different fertilizations were not obvious. Chemical fertilizers combined with straw or manure can increase ultraviolet spectrum absorption values of DOM (SUVA₂₅₄ and SUVA₂₆₀ and SUVA₂₈₀) and α (355) in 0~20 cm soil layer, and decrease Ultraviolet spectrum absorption ratios of soil DOM (A₂₅₀/A₃₆₅). It showed that the fragrance, hydrophobicity, molecular weight and CDOM increased. Meanwhile, it was not obvious in 20~40 and 40~60 cm soil layers. A₃₀₀/A₄₀₀ in different soil layers was greater than 3.5, and it showed this soil was rich in Fulvic Acid. Long term chemical fertilizers combined with manure and straw can increase DOM content in 0~20 and 20~40 cm soil layers, decrease C/N, and increase soil fertility. Meanwhile, it also can increase the conjugated structure, humus, fragrance, hydrophobicity and molecular weight of DOM in 0~20 cm soil layer. Long term fertilization has less effects on soil DOM content and structure in 40~60 cm soil layer.