AMINO-ACID-COMPOSITION OF SOIL ORGANIC-MATTER

This study investigated the amino acid composition of soil organic mat ter extracted from ten surface soils in addition to surface soils from two long-term cropping systems [continuous corn (CCCC), corn-soybean- corn-soybean (CSCS), and corn-oats-meadow-meadow (COMM)] at two sites in Iowa: the Clarion-Webster Research Center (CWRC) and the Galva-Prim ghar Research Center (GPRC). Results showed that, with the exception o f asparagine pluse aspartic acid and glutamine plus glutamic acid, the other 13 amino acids studied, expressed as perecentages of total amin o acids extracted, were generally very uniform among the soils. The to tal amino acids extracted from the ten soils were significantly correl ated with organic carbon (C) (r=0.79;P<0.01) and clay content (r=0.76; P<0.01), but not with total nitrogen (N), pH, or sand content. Express ed as percentages or organic C and N in soils, the amounts extracted r anged from 10.9% to 32.4% and from 12.0% to 27.4%, respectively. The a mino acid N identified, expressed as percentages of organic N extracte d, ranged from 32% to 50% and the C/N ratios of the extracted organic matter ranged from 10.1 to 14.9. The type of rotation did not signific antly affect the total amino acid content of the soils from the same N treatment, but it did affect the total amino acid content of soils fr om the control plots. The total amino acids measured under the differe nt crop rotations at the CWRC site were in the order: COMM>CCCC>CSCS. The order for the GPRC site was: CSCS>COMM>CCCC. The amino acid N iden tified, expressed as percentages of organic N extracted from soils at the CWRC site, ranged from 33.1% to 50% and for the GPRC site ranged f rom 26.5% to 51.4%. The C/N ratios of the organic matter extracted ran ged from 10.4 to 14.1 and from 6.5 to 14.3 for the soils from CWRC and GPRC sites, respectively.