Concentration and composition of soil amino compounds in major Chinese croplands.

The importance of organic nitrogen (N) in soil N cycle is difficult to assess because of uncertainties regarding its composition, sources, and bioavailability. The objective of this study was to characterise the distribution of soil inorganic N and amino compounds in major Chinese croplands. Results demonstrated that soil extractable N composition was dominated by inorganic N (), and the contents of different N forms widely varied across the 11 different soils. Free amino acid contents ranged from 0.26 to 1.03 mg N kg−1. In contrast, soil-adsorbed amino acids were approximately seven times greater than the free amino acids, which likely represent a potential important pool for free amino acids. Pearson analysis showed that soil free and -adsorbed amino acids were negatively related to soil pH (r = −.39 to −.81,p < .05), while extractable total N,, and hydrolysable amino acids showed the opposite trends. Irrespective of the significant differences in soil properties and environment, soil major amino acid composition was similar, with seven dominant amino acids: alanine, glycine, glutamic acid, aspartic acid, serine, threonine, and isoleucine. The similar composition suggests that the production and utilisation of amino acids likely rely on the same biochemistry or similar amino acid constituents. [ABSTRACT FROM AUTHOR]

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