科研之友
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摘要
the organic n forms in soil are determined by identification and quantification of organic compounds released by acid hydrolysis. there are no available data on the chemical nature of organic n in the amazon soils. the objective of this study was to identify and quantify the transformation of 15n-labeled nitrogen fertilizers to different organic nitrogen fractions in three soils of central amazonia: an oxisol, an ultisol and a low-humic gley (lhg). the soils were sampled after cultivation in greenhouse experiment. the chemical fractionation of soil organic nitrogen, as acid-hydrolysable and distillable n (nsad), acid-hydrolysable non-distillable n (nsand) and non-hydrolysable n (nnh), was performed. in the oxisol and ultisol, 63 to 66% and 69 to 73%, respectively, of fertilizer n applied was incorporated in the nsand fraction. this suggests that n immobilization of microbial origin is important in these soils. in the lhg, there was equal immobilization in both nsand and nsad fractions: 46 to 53% of n applied was immobilized in nsand, while 42 to 53% was immobilized in nsad. in this soil, the presence of 2:1 type clays probably contributed to the high stock of 15n incorporated in the nsad fraction, due to fixation of nh4+.
