Influence of land use on the characteristics of humic substances in some tropical soils of Nigeria

In highly weathered tropical conditions, soil organic matter is important for soil quality and productivity. We evaluated the effects of deforestation and subsequent arable cropping on the qualitative and quantitative transformation of the humic pool of the soil at three locations in Nigeria. Cultivation reduced the humic pool in the order: acetone‐soluble hydrophobic fraction (HE) > humic acid (HA) > humin (HU) > fulvic acid (FA), but not to the same degree at all three sites. The C and N contents, as well as the C/N ratios of humic extracts, were large and not substantially influenced by land use. The δ13C values of the humic extracts were invariably more negative in forested soils thereby showing a dilution of δ13C signature with cultivation from C3 to C4 plants. The δ13C values of apolar HE fractions were generally more negative, indicating a reduced sensitivity compared with other humic fractions to turnover of crop residues. The contents of hydrophobic constituents (alkyl and aromatic C), as revealed by cross‐polarization magic angle spinning (CPMAS) 13C‐NMR spectroscopy, in HA, FA and HU were generally < 50%, with the exception of larger hydrophobicity in HU in the forested soil at Nsukka and HA in that at Umudike. The HE fraction contained significantly more apolar constituents, and consequently had a larger intrinsic hydrophobicity than the other humic fractions. The larger reduction of apolar humic constituents than of the less hydrophobic humic fractions, when these soils were deforested for cultivation, indicates that at those sites the stability of accumulated organic matter is to be ascribed mainly to the selective preservation of hydrophobic compounds.

[1]  R. Spaccini,et al.  Carbohydrates and aggregation in lowland soils of Nigeria as influenced by organic inputs , 2004 .

[2]  A. Piccolo,et al.  COMMENTS ON “MODERN ANALYTICAL STUDIES OF HUMIC SUBSTANCES” BY HATCHER ET AL. , 2003 .

[3]  A. Piccolo.  The supramolecular structure of humic substances: A novel understanding of humus chemistry and implications in soil science , 2002 .

[4]  A. Piccolo.  THE SUPRAMOLECULAR STRUCTURE OF HUMIC SUBSTANCES , 2001 .

[5]  R. Spaccini,et al.  Carbohydrates in water-stable aggregates and particle size fractions of forested and cultivated soils in two contrasting tropical ecosystems , 2001 .

[6]  R. Spaccini,et al.  Transformation of organic matter from maize residues into labile and humic fractions of three European soils as revealed by 13C distribution and CPMAS‐NMR spectra , 2000 .

[7]  A. Quiroga,et al.  FULVIC ACID CARBON AS A DIAGNOSTIC FEATURE FOR AGRICULTURAL SOIL EVALUATION , 2020 .

[8]  R. Spaccini,et al.  Increased Sequestration of Organic Carbon in Soil by Hydrophobic Protection , 1999, Naturwissenschaften.

[9]  A. Piccolo,et al.  Atrazine Interactions with Soil Humic Substances of Different Molecular Structure , 1998 .

[10]  E. J. Kamprath,et al.  A comparison of the contributions of clay, silt, and organic matter to the effective CEC of soils in Sub-Saharan Africa , 1998 .

[11]  P. Albrecht,et al.  A novel pathway of soil organic matter formation by selective preservation of resistant straight-chain biopolymers: chemical and isotope evidence , 1998 .

[12]  S. Archer,et al.  δ13C values of soil organic carbon and their use in documenting vegetation change in a subtropical savanna ecosystem , 1998 .

[13]  M. Bernoux,et al.  The use of stable carbon isotopes for estimating soil organic matter turnover rates , 1998 .

[14]  A. Piccolo,et al.  Quantitative aspects of solid-state 13C-NMR spectra of humic substances from soils of volcanic systems. , 1997 .

[15]  G. Guggenberger,et al.  Factors controlling humification and mineralization of soil organic matter in the tropics , 1997 .

[16]  C. Feller,et al.  Physical control of soil organic matter dynamics in the tropics , 1997 .

[17]  J. Diels,et al.  A comparison of the contributions of clay, silt, and organic matter to the effective CEC of soils of subsaharan Africa , 1997 .

[18]  A. Piccolo.  Humus and Soil Conservation , 1996 .

[19]  G. Guggenberger,et al.  Organic Matter Dynamics in Forest Soils of Temperate and Tropical Ecosystems , 1996 .

[20]  R. Newman,et al.  A long-term effect of N fertilization on the 13C CPMAS NMR of de-ashed soil humin in a second-growth Douglas-fir stand of coastal British Columbia , 1995 .

[21]  P. Puget,et al.  Total and young organic matter distributions in aggregates of silty cultivated soils , 1995 .

[22]  L. Tieszen,et al.  Carbon Isotope Dynamics During Grass Decomposition and Soil Organic Matter Formation , 1995 .

[23]  B. Ellert,et al.  Turnover of soil organic matter and storage of corn residue carbon estimated from natural 13C abundance , 1995 .

[24]  I. Lepsch,et al.  Carbon storage and other properties of soils under agriculture and natural vegetation in São Paulo State, Brazil , 1994 .

[25]  T. Desjardins,et al.  Organic carbon and 13C contents in soils and soil size-fractions, and their changes due to deforestation and pasture installation in eastern Amazonia , 1994 .

[26]  J. Portal,et al.  Influence of content and nature of organic matter on the structure of some sandy soils from West Africa , 1993 .

[27]  I. Kögel‐Knabner,et al.  Nature and distribution of alkyl carbon in forest soil profiles: implications for the origin and humification of aliphatic biomacromolecules , 1992 .

[28]  D. Jenkinson,et al.  Decomposition of carbon-14 labeled ryegrass and maize under tropical conditions , 1990 .

[29]  P. Lavelle,et al.  Estimate of organic matter turnover rate in a savanna soil by 13C natural abundance measurements. , 1990 .

[30]  B. Fry,et al.  Controls on Natural Nitrogen‐15 and Carbon‐13 Abundances in Forest Soil Organic Matter , 1988 .

[31]  N. Agbim.  Dry Season Decomposition of Leaf Litter from Five Common Plant Species of West Africa , 1987 .

[32]  D. Cassel,et al.  EFFECT OF LAND‐CLEARING METHODS AND POSTCLEARING MANAGEMENT ON AGGREGATE STABILITY AND ORGANIC CARBON CONTENT OF A SOIL IN THE HUMID TROPICS , 1986 .

[33]  A. Page.  Methods of soil analysis. Part 2. Chemical and microbiological properties. , 1982 .

[34]  B. Volkoff,et al.  Distribution de l'isotope stable 13C dans la matière organique d'un sol ferrallitique de l'Etat de Bahia (Brésil) , 1977 .

[35]  I C Edmundson,et al.  Particle size analysis , 2013 .