Abstract:

Cultivation of native land can reduce the quality of soil by decreasing topsoil contents of organic carbon, total nitrogen, and phosphorus in the semiarid Pampas of Argentina. The objective of this study was to analyze the changes produced by cultivation on organic carbon (OC), total nitrogen (TN) and phosphate (inorganic and organic fractions) in two aggregate sizes of three different semiarid soils of Argentina as a function of soil depth. The study was carried out on three soils (loamy Hapludoll, loamy Haplustoll and sandy loam Haplustoll), with two uses compared at each site. Generally, the Caldenal savanna-like ecosystem (native soil) and a cultivated counterpart with annual crops for more than 60 years (cultivated soil) were compared. Results showed that all soils had similar distribution patterns with depth of OC, TN, total inorganic phosphorus (Pi), organic phosphorus (Po) and available phosphorus (Pa) in the 100-2000 μm and < 100 μm aggregates of both the native and cultivated soils. Contents of OC, TN and Pi in the whole soil (< 2000 μm) decreased sharply with depth in native soils (OC: 50%, TN: 45% and Pi: 23%), but they had a more homogeneous distribution in cultivated soils. These tendencies were attributed to the stratification occurring in non-disturbed native soils and the mixing of the upper 20 cm in cultivated soils. Cultivation produced losses of OC (73%) and Po (64%) from the 100-2000 μm aggregates at both depths in the sandy loam Haplustoll, while it produced losses of TN (52%) and Pi (42%) from the < 100 μm aggregates in the upper 10 cm of the loamy Hapludoll. OC and Po losses of the sandy loam Haplustoll were probably produced by the mineralization of organic compounds, whereas TN and Pi losses of the loamy Hapludoll were produced by wind erosion and plant uptake. Larger relative decreases of OC and Po than TN in coarse aggregates (100-2000 μm) and Pi in fine aggregates (< 100 μm) with cultivation indicate that coarse aggregates are less stable than fine aggregates (< 100 μm), and therefore more sensitive to changes in soil quality due to changes in land use. We concluded that management practices that tend to improve the formation of large aggregates as no-till or permanent pastures should be used in coarse textured Haplustolls in order to prevent large OC and Po losses. Management practices that include soil plowing will produce a breakdown of coarse aggregates and will moderately decrease OC, Po, TN, Pa and Pi contents in loamy Haplustolls and Hapludolls. Nevertheless, the destruction of coarse aggregates will increase the risk of losses of these elements by wind erosion.

Author affiliation: Ana María, Urioste. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Hevia, Graciela Gloria. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Hepper, Estela Noemí. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Anton, L. E.. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Bono, A. A.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina

Author affiliation: Buschiazzo, Daniel Eduardo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina

Abstract:

The biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) are interlinked by primary production, respiration and decomposition in terrestrial ecosystems. It has been suggested that the C, N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes. Climatic controls on biogeochemical cycles are particularly relevant in arid, semi-arid and dry sub-humid ecosystems (drylands) because their biological activity is mainly driven by water availability. The increase in aridity predicted for the twenty-first century in many drylands worldwide may therefore threaten the balance between these cycles, differentially affecting the availability of essential nutrients. Here we evaluate how aridity affects the balance between C, N and P in soils collected from 224 dryland sites from all continents except Antarctica. Wefind a negative effect of aridity on the concentration of soil organic C and total N, but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover, which may favour the dominance of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition1. Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands, but increase that of P. These changes would uncouple the C, N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems.

Author affiliation: Delgado Baquerizo, Manuel. Universidad Pablo de Olavide; España. Universidad Rey Juan Carlos. Departamento de Biología y Geología. Área de Biodiversidad y Conservación; España

Author affiliation: Maestre, Fernando T.. Universidad Pablo de Olavide; España. Universidad Rey Juan Carlos. Departamento de Biología y Geología. Área de Biodiversidad y Conservación; España

Author affiliation: Gallardo, Antonio. Universidad Pablo de Olavide; España

Author affiliation: Bowker, Matthew A.. Northern Arizon University/school Of Forestry;

Author affiliation: Wallenstein, Matthew D.. Northern Arizona University; Estados Unidos

Author affiliation: Bran, Donaldo Eduardo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina. Universidad Rey Juan Carlos. Departamento de Biología y Geología. Área de Biodiversidad y Conservación; España

Author affiliation: Gatica, Mario Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina

Author affiliation: Hepper, Estela Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Prina, Anibal Oscar. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Pucheta, Eduardo Raúl. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina

Author affiliation: Huber Sannwald, Elisabeth. Instituto Potosino de Investigación Científica y Tecnológica; México

Author affiliation: Jankju, Mohammad. Ferdowsi University of Mashhad; Irán

Author affiliation: Liu, Jushan. Northeast Normal University. Institute of Grassland Science,; China

Author affiliation: Mau, Rebecca L.. Northern Arizona University; Estados Unidos

Author affiliation: Miriti, Maria. Ohio State University; Estados Unidos

Author affiliation: Monerris, Jorge. Université du Québec a Montreal; Canadá

Author affiliation: Naseri, Kamal. Ferdowsi University of Mashhad; Irán

Author affiliation: Noumi, Zouhaier. Université de Sfax; Túnez

Author affiliation: Polo, Vicente. Universidad Rey Juan Carlos. Departamento de Biología y Geología. Área de Biodiversidad y Conservación; España

Author affiliation: Ramírez Collantes, David A.. International Potato Center; Perú

Author affiliation: Romão, Roberto. Universidade Estadual de Feira de Santana. Departamento de Ciencias Biológica, Herbario; Brasil

Author affiliation: Tighe, Matthew. University of New England; Australia

Author affiliation: Torres, Duilio. Universidad Centroccidental ‘‘Lisandro Alvarado’’; Venezuela

Author affiliation: Torres Díaz, Cristian. Universidad del Bio Bio. Facultad de Ciencias. Departamento de Ciencias Básicas. Laboratorio de Genómica y Biodiversidad; Chile

Author affiliation: Ungar, Eugene D.. The Volcani Center. Agricultural Research Organization. Institute of Plant Sciences; Israel

Author affiliation: Val, James. Office of Environment and Heritage; Australia

Author affiliation: Wamiti, Wanyoike. National Museums of Kenya. Zoology Department; Kenia

Author affiliation: Wang, Deli. Northeast Normal University. Institute of Grassland Science; China

Author affiliation: Zaady, Eli. Gilat Research Center; Israel

Abstract:

Previous results showed that phosphorus sorption strongly correlated with contents of active Al and Fe oxides and organic matter (OM) in soils of the-Semiarid Argentinean Pampas. Objective of this study was to determine the relative influence of these soil compounds on P sorption. It was hypothesized that contents of OM and Al and Fe oxides should decrease P sorption in the studied soils. With this purpose, sorption isotherms were carried out on non treated soils and on soils samples pre-treated with H2O2 (OM destruction), acid oxalate (AcOx, destruction of amorphous oxides) and boiled acid oxalate (BAcOx, destruction of crystalline oxides). Results showed that OM destruction did not affect none of the constants deduced from Freundlich isotherm (a, l/b and BCO.3). This was probably due to the variable effect of OM on these constants in each soil. On the other hand, constant a decreased 20 to 88% after elimination of crystalline oxides, and 17 to 48% after elimination of amorphous oxides, BCO.3 decreased 33 to 87% after elimination of crystalline oxides, and 21 to 44% after elimination of amorphous oxides, and 1/b remained unchanged. Such results indicate that P sorption (a), as well as the ability of the soil to liberate P to the soil solution (BCO.3), were highly influenced by the amount of amorphous and crystalline Al and Fe oxides and that the retention energy of P (1/b) remained unchanged.

Author affiliation: Hevia, Graciela Gloria. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Hepper, Estela Noemí. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Buschiazzo, Daniel Eduardo. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Peinemann, Norman. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina

Abstract:

Nutrient and organic carbon (OC) losses are important components of the soil degradation processes produced by continuous agriculture. It was hypothesized that coarse textured soils will be more affected by cultivation than tine textured ones. The purpose of this study was to evaluate the status of OC, total nitrogen (Nt), and three phosphorous fractions (total inorganic, Pi; organic, Po; and available, Pa) in different textured virgin (under Prosopis caldenia forest) and cultivated soils of the semi-arid pampa of Argentina. Three virgin and non-fertilized cultivated soil pairs, representative from soils of the region, were selected for this study: two tine sandy loam Entic Haplustolls and a sandy Typic Ustipsamment. The element content of each soil was analysed from the < 0.1-mm to 0.1-2-mm sized aggregates. Results indicated that cultivation decreased the OC, Po and Pi contents in tine aggregates of the tine textured soils, and in coarse aggregates of the coarse textured soil. Plant absorption and wind erosion were probably the main processes which decreased element contents in both textural soil types. It was speculated that in the sandy soil the elements lost from tine sized aggregates were restored by the break down of the weak coarse aggregates produced by tillage. The C/N ratios showed mostly small changes due to cultivation, indicating that no changes of organic matter quality occurred. Only the sandy soil showed C/N increases in the tine sized aggregates and decreases in the coarse sized aggregates. The C/Po quotients were not changed by cultivation, indicating that the qualitative composition of P organic compounds remained unchanged. Large OC decreases and Pa increases after cultivation detected in one of the tine textured soil were apparently linked to the occurrence of natural fires. © 2001 Academic Press.

Author affiliation: Buschiazzo, Daniel Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina

Author affiliation: Hevia, Graciela Gloria. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Hepper, Estela Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Ana María, Urioste. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Bono, Alfredo A.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina

Author affiliation: Babinec, Francisco José. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina

Abstract:

Soil organic matter contents (SOM) of soils of the Semiarid Pampas of Argentina (SAP), mostly Entic Haplustolls, increase with the amount of silt+clay, but it is still not known how soil texture affects its qualitative composition in interaction with climatic and management conditions. Because of that the organic matter content of the following aggregate size fractions were determined: <2000 μm (SOM), 100-2000 μm (YOM), <100 μm (HOM), water floatable organic matter (FOM), and the E4/E6 quotient. These fractions were studied in the 20-cm topsoils of seven REFERENCE (virgin Caldenal savanna-like soils), and 10 CULTIVATED soils (under continuous conventional tillage since more than 50 years). Results showed that SOM of both REFERENCE and CULTIVATED soils was mainly composed by YOM (57%), and to a lesser extent by HOM (37%) and FOM (5%). Silt+clay conditioned positively the contents of SOM, YOM and HOM of both REFERENCE (R2=0.18, R2=0.21, R 2=0.21, respectively, n=21, p<0.05) and CULTIVATED soils (R 2=0.62, R2=0.44, R2=0.52, respectively, n=30, p<0.001). The positive relationship existing between silt+clay and both SOM and YOM seems to be not longer valid in sites with mean annual temperatures (MAT) higher than 17°C. YOM and HOM accumulation were positively affected by precipitation and negatively by temperature in combination with silt+clay. This effect was more pronounced for HOM. The slopes of the regressions between SOM, HOM and YOM with silt+clay were more pronounced for REFERENCE soils than for CULTIVATED soils, indicating the largest absolute losses of these organic matter fractions in fine- rather than in coarse-textured soils. E4/E6 quotients were lower than 5 in all studied soils indicating that humic rather than fulvic acids exist in the well humified organic fraction of the studied soils. Contents of FOM and E4/E6 values did not correlated with the climatic conditions nor with soil texture or management. Potential SOM losses can be larger in fine-textured soils (up to 54.3 Mg C ha-1) than in coarse-textured (up to 35.7 Mg C ha-1). Probable changes of soil texture by wind erosion will modify absolute contents of SOM, YOM and HOM, while modifications of temperature or rains regimes will affect HOM more.

Author affiliation: Hevia, Graciela Gloria. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Buschiazzo, Daniel Eduardo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina

Author affiliation: Hepper, Estela Noemí. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Ana María, Urioste. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Author affiliation: Antón, E. L.. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina