Analysis of organic fractions as indicators of soil quality under natural and cultivated systems

Matias Duval, Juan A. Galantini, Julio O. Iglesias, Silvia Canelo, Juan M. Martinez, Luis Wall

Soil organic matter (SOM) or carbon (SOC) is the most important component of the soil and it is composed of fractions with different lability. Particulate organic carbon (POC) and soluble carbohydrates (CHs), among others, are the most sensitive to changes in crops and soil management practices. The purpose of this study was to analyze different soil parameters aimed for the evaluation of management practices under widely different soil and climatic conditions. Soils were located along a West-East transect in the most productive region of the Argentinean pampas: [West] Bengolea and Monte Buey (Córdoba), Pergamino (Buenos Aires) and Viale (Entre Rios) [East]. Three treatments were defined according to land use: “Good agricultural practices” (GAP): sustainable agricultural management under no-till; “Poor agricultural practices” (PAP): non-sustainable agricultural management under no-till; “Natural environment” (NE): rangelands long as reference situation. Samples were taken at 0-10 and 10-20 cm depths. SOC was determined in different particle fractions: 0.1-2.0 mm (coarse particulate organic carbon, POC_c), 0.053-0.10 mm (fine particulate organic carbon, POC_f), and 0-0.053 (mineral-associated organic carbon, MOC). Total (CH_t) and soluble (CH_s) carbohydrate contents were also determined. The SOC level in NE was decreasing from the East (27.3 g kg^-1 in Viale) to the West (13.3 g kg^-1 in Bengolea), following the rainfall and texture gradient among sites. The POC_c/SOC and POC_c + POC_f / SOC ratios in the NE showed differences among sites, suggesting different dynamic depending on the environmental characteristics of different locations. The SOC levels in the upper layer of agricultural soils were 16 to 44% lower than those of natural ones; the differences were lower in clayed and sandy soils. Carbon stocks were estimated for an equivalent mass of soil (950 and 2350 Mg ha^-1) in order to consider differences in bulk densities among different treatments. Mean values were significantly different (p<0.001) for the different management practices: NE (26.6 Mg ha^-1) > GAP (20.1 Mg ha^-1) > PAP (16.3 Mg ha^-1). In general, labile organic fractions showed differential sensibility. Fractions with an intermediate dynamic, as POC_f (53-100 µm) and CH_t, seem to be better indicators to detect the short- and medium-term management effects than high dynamic fractions.

Keywords: Soil organic carbon, Soil organic fractions, No-tillage, Good Agricultural Practices, Soil quality

Duval M.E., J.A. Galantini, J.O. Iglesias, S. Canelo, J.M. Martinez, L. Wall. 2013. Analysis of organic fractions as indicators

 of soil quality under natural and cultivated systems. Soil and Tillage Research 131: 11-19.

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