Influence of texture on organic matter distribution and quality and nitrogen and sulphur status in semiarid Pampean grassland soils of Argentina

Texture, among several other factors, may play an important role in controlling the distribution and activity of soil microbial biomass and, in turn, the size and quality of soil organic matter (SOM) pools, and the related dynamics of N and S in soil. Little information is available in the current literature on the occurrence and extent of these textural effects in semiarid soils of Argentinean Pampas. Separation of the primary SOM pools by particle-size fractionation were expected to contribute to elucidate how different SOM fractions could be affected by texture in Pampean soils. The main objective of this study was to evaluate the amount, quality and distribution of SOM fractions, either physically separated, i.e., particulate and mineral-associated SOM, or chemically separated, i.e. the humic acid (HA) and fulvic acid (FA) fractions of SOM, in the whole soil and fine fractions (silt and clay) of variously textured soils from semiarid grasslands in the Argentinean Pampas region. Furthermore, the influence of texture was investigated on the N and S status and distribution, also in relation to SOM fractions. The content of any SOM fraction showed a highly positive correlation with the fine fraction content of the parent soil. The amounts of N and S in particulate SOM were not affected by soil textural differences, whereas they decreased in the fine fractions and in HAs with increasing content of soil fine fractions. Fine-textured soils contained an amount of total N and S, possibly mobilized from SOM components of the fine fraction including HAs, which was larger than that occurring in coarse-textured soils. The HAs in the fine fractions of fine-textured soils featured a degree of aromatic polycondensation, a level of conjugated chromophores and a humification degree larger, and a molecular heterogeneity smaller than those of HAs isolated from the fine fractions of coarse-textured soils. An opposite trend was exhibited by the corresponding FAs. In conclusion, soil texture appeared to have an important impact on the amount, distribution and chemical properties of the various SOM components, and especially the HA and FA fractions, in Pampean grassland soils. As well, S and N mobility and availability in these soils was markedly influenced by textural differences.

[1]  W. Parton,et al.  Analysis of factors controlling soil organic matter levels in Great Plains grasslands , 1987 .

[2]  B. D. Kay,et al.  Conservation tillage and depth stratification of porosity and soil organic matter , 2002 .

[3]  L. Brussaard,et al.  Relationships between soil texture, physical protection of organic matter, soil biota, and c and n mineralization in grassland soils , 1993 .

[4]  R. Lavado,et al.  Climate, organic matter and clay content relationships in the Pampa and Chaco soils, Argentina , 1998 .

[5]  A. Franzluebbers,et al.  ACTIVE FRACTIONS OF ORGANIC MATTER IN SOILS WITH DIFFERENT TEXTURE , 1996 .

[6]  K. A. Horton,et al.  Soil organic matter dynamics in paired rangeland and cropland toposequences in North Dakota , 1985 .

[7]  L. Brussaard,et al.  Relationships between habitable pore space, soil biota and mineralization rates in grassland soils , 1993 .

[8]  G. Gee,et al.  Particle-size Analysis , 2018, SSSA Book Series.

[9]  B. Christensen.  Physical Fractionation of Soil and Organic Matter in Primary Particle Size and Density Separates , 1992 .

[10]  J. Oades,et al.  Decomposition of plant material in Australian soils. III. Residual organic and microbial biomass C and N from isotope-labelled legume material and soil organic matter, decomposing under field conditions , 1985 .

[11]  E. T. Elliott,et al.  Soil textural control on decomposition and soil organic matter dynamics , 1996 .

[12]  D. Coleman,et al.  Let the soil work for us , 1988 .

[13]  D. Sparks,et al.  Methods of soil analysis. Part 3 - chemical methods. , 1996 .

[14]  Peter Kuikman,et al.  Soil structural aspects of decomposition of organic matter by micro-organisms , 1990, Biogeochemistry.

[15]  N. Scott,et al.  Factors Controlling Soil Carbon Levels in New Zealand Grasslands Is Clay Content Important , 2000 .

[16]  J. Oades,et al.  The retention of organic matter in soils , 1988 .

[17]  Yona Chen,et al.  Information Provided on Humic Substances by E4/E6 Ratios1 , 1977 .

[18]  J. Groot,et al.  Modelling organic matter dynamics in different soils. , 1990 .

[19]  V. D'Orazio,et al.  Characteristics of humic acids of some Venezuelan soils , 1998 .

[20]  R. H. Bray,et al.  DETERMINATION OF TOTAL, ORGANIC, AND AVAILABLE FORMS OF PHOSPHORUS IN SOILS , 1945 .

[21]  David S. Schimel,et al.  Texture, climate, and cultivation effects on soil organic matter content in U.S. grassland soils , 1989 .

[22]  J. Hassink,et al.  Effect of soil texture on the size of the microbial biomass and on the amount of c and n mineralized per unit of microbial biomass in dutch grassland soils , 1994 .

[23]  K. Stahr,et al.  Patterns of Organic Matter Accumulation in Soils of the Semiarid Argentinian Pampas , 1991 .

[24]  A. Klute.  Methods of soil analysis. Part 1. Physical and mineralogical methods. , 1988 .

[25]  B. A. Stewart,et al.  Advances in Soil Science , 1986, Advances in Soil Science.

[26]  R. Lal,et al.  Soil organic carbon dynamics in native and cultivated ecosystems of South America. , 1998 .

[27]  T. Miano,et al.  CHARACTERIZATION, DIFFERENTIATION, AND CLASSIFICATION OF HUMIC SUBSTANCES BY FLUORESCENCE SPECTROSCOPY , 1991 .

[28]  F. J. Stevenson.  HUmus Chemistry Genesis, Composition, Reactions , 1982 .

[29]  A. Spain.  Influence of environmental conditions and some soil chemical properties on the carbon and nitrogen contents of some tropical Australian rainforest soils , 1990 .

[30]  G. S. Campbell,et al.  Low temperature or low water potemntial effects on the mictobial decomposition of wheat residue , 1986 .