HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (20) Citing Articles via Google Scholar Google Scholar Articles by Olk, D.C. Articles by Senesi, N. Search for Related Content PubMed Articles by Olk, D.C. Articles by Senesi, N. GeoRef GeoRef Citation Agricola Articles by Olk, D.C. Articles by Senesi, N.

DIVISION S-2-SOIL CHEMISTRY

Decrease in Humification of Organic Matter with Intensified Lowland Rice Cropping

A Wet Chemical and Spectroscopic Investigation

^a IRRI, P.O. Box 3127, Makati Central Post Office (MCPO), 1271 Makati City, Philippines
^b Istituto di Chimica Agraria, Università di Bari, Via Amendola, 165/A, 70126 Bari, Italy

d.olk{at}cgiar.org

To address recent concerns of impaired nutrient cycling in intensively cropped lowland rice soils of tropical Asia, we have been investigating the effects of continuous rice cropping on the chemical nature of soil organic matter (SOM). In this study, the labile mobile humic acid (MHA) fraction and the more recalcitrant calcium humate (CaHA) fraction were extracted from soils of four long-term field trials on the International Rice Research Institute (IRRI) farm, which varied in the number of annual irrigated rice crops and hence degree of soil submergence. The two humic acid (HA) fractions were analyzed by Fourier-transform infrared, fluorescence, and electron spin resonance spectroscopies for elemental composition and acidic functional groups. With increasing soil submergence, the HA fractions became less oxidized or humified, with higher S and H and lower O concentrations, more amide or amino, hydroxyl, and methoxy groups, and fewer carboxyl groups and organic free radicals. The HA extracted from submerged soils appeared to have greater capacity for complexing Cu⁺², Fe⁺³, and VO⁺² than did HA from aerated soils. Fertilizer treatments had little effect on HA chemical structure. The MHA was less humified than the CaHA, having fewer acidic functional groups, smaller C:N and C:H ratios, richer concentrations of amides and carbohydrates, lower concentrations of COOH, higher fluorescence intensity, and shorter wavelength of fluorescence emission maximum, and lower concentration of organic free radicals. Free radical concentrations for both HA fractions were highly correlated with other indices of humification reported here and elsewhere.

Abbreviations: CaHA, calcium humate • ESR, electron spin resonance • FRS, fresh rice straw • FT IR, Fourier-transform infrared • LTCCE, long-term continuous cropping experiment • MHA, mobile humic acid • NMR, nuclear magnetic resonance • PU, prilled urea • RFI, relative fluorescence intensity • SOM, soil organic matter

This article has been cited by other articles:

				M. F. Pampolino, E. V. Laureles, H. C. Gines, and R. J. Buresh Soil Carbon and Nitrogen Changes in Long-Term Continuous Lowland Rice Cropping Soil Sci. Soc. Am. J., May 1, 2008; 72(3): 798 - 807. [Abstract] [Full Text] [PDF]

				Z. He, T. Ohno, B. J. Cade-Menun, M. S. Erich, and C. W. Honeycutt Spectral and Chemical Characterization of Phosphates Associated with Humic Substances Soil Sci. Soc. Am. J., August 22, 2006; 70(5): 1741 - 1751. [Abstract] [Full Text] [PDF]

				D. C. Olk A Chemical Fractionation for Structure-Function Relations of Soil Organic Matter in Nutrient Cycling Soil Sci. Soc. Am. J., April 19, 2006; 70(3): 1013 - 1022. [Abstract] [Full Text] [PDF]

				F. Fares, A. Albalkhi, J. Dec, M. A. Bruns, and J.-M. Bollag Physicochemical Characteristics of Animal and Municipal Wastes Decomposed in Arid Soils J. Environ. Qual., July 5, 2005; 34(4): 1392 - 1403. [Abstract] [Full Text] [PDF]

				N. B. Ve, D. C. Olk, and K. G. Cassman Characterization of Humic Acid Fractions Improves Estimates of Nitrogen Mineralization Kinetics for Lowland Rice Soils Soil Sci. Soc. Am. J., July 1, 2004; 68(4): 1266 - 1277. [Abstract] [Full Text] [PDF]

				N. Mahieu, D.C. Olk, and E.W. Randall Multinuclear Magnetic Resonance Analysis of Two Humic Acid Fractions from Lowland Rice Soils J. Environ. Qual., March 1, 2002; 31(2): 421 - 430. [Abstract] [Full Text] [PDF]