长期施肥条件下土壤养分的动态和平衡——Ⅱ.对土壤氮的有效性和腐殖质氮组成的影响

长期施用有机肥、化肥或二者配合施用均增加了土壤全氮、碱解氮、酸解氮和植物吸收氮量,提高了土壤氮的有效性,其后效可保持至第3年;土壤腐殖质的胡敏酸氮减少,富里酸氮增加。富里酸氮易被6mol/L HCl水解,水解氮占71.4％～74.2％;胡敏酸氮比较稳定,水解氮占40％～45％。在水解氮中,氨基氮的比例为2/3～3/4,铵态氮为1/4～1/3。胡敏酸中非水解氦的主要成分是杂环化合物氮(37.5％～52.5％),其次是苯系化合物氮(31％～35.2％)和非苯系化合物氮(10.6％～26.7％)。长期施用有机肥和化肥,杂环氮比例减少,苯系和非苯系化合物氮比例增加。胡敏酸表层氮占1/3左右,核心氮占2/3左右,施用有机肥和化肥,胡敏酸表层氮增加,核心氮降低。

DYNAMIC AND BALANCE OF SOIL NUTRIENTS UNDER LONG-TERM FERTILIZATION CONDITIONS Ⅱ. Effect on N availability and composition of humus N

Long term application of organic manure, or inorganic fertilizers, or combination, of the two forms increased total nitrogen (N), alkali-hydrolyzed N and acid-hydrolyzed N in the soil, stimulated soil N availability and plant uptake. Its residual effect could be found in the third years after fertilization. As the soil humus, humic acid-N reduced, while fulvic acid-N increased due to fertilization. The fulvic acid-N can be easily hydrolyzed in 6mol/L HC1 solution, 71.4% ~ 74.2% of the total fulvic acid-N was hydrolyzed. The humc acid-N is more stable than fulvic acid-N, only 40%~45% of humic acid-N can be hydrolyzed in the HC1 solution. As the form of hydrolyzed N, 2/3~3/4 was amino-N while l/4~1/3 was NH4-N.The majority of the unhydrolyzed N in the humic acid was heterocyclic compound- N (37.5% - 52.5%), followed by benzene compound-N (31. 0%~35. 2%) and non-benzene compound-N (10. 6%~26. 7%). Due to long term application of organic manure and inorganic fertilizers, the portion of N in heterocyclic compound was reduced, while benzene and non-benzene compound was increased. About 1/3 of humic acid-N was on the surface, while 2/3 was in core. Application of organic and inorganic fertilizers increased the amount of N on humic acid surface, and reduced that in core of the humic acid.