Soil management effects on organic matter fractions and physical properties in Rolling Pampa of Argentina

ALVAREZ, C. R.; TABOADA M. A.; GUTIÉRREZ BOEM F. H.; BONO, A.; FERNÁNDEZ, P. L.; PRYSTUPA, P.

Poitiers

Simposio; International Symposium on Organic Matter Dynamics in Agro-Ecosystems; 2007

The assessment of soil quality is key in soils from temperate plains, which are subjected to great productive pressures to meet the increasing global food demand.  This work aims at: a) evaluating soil quality at a regional scale under different managements in the Rolling Pampa of Argentina; and b) finding a minimum dataset characterizing soil physical quality in this temperate plain. Thirty-nine loamy, silty loamy and silty clay loamy soils were sampled in conventionally tilled (CT), no tilled (NT), and nondisturbed management regimes. The thickness of A horizon did not differ among soil textural groups, and was 4 cm (p < 0.1) thicker in nondisturbed than in CT and NT soils.  Most studied soil properties (total and particulate organic carbon, topsoil bulk density and relative compaction) varied significantly from nondisturbed to  CT and NT soils. Total and particulate soil organic carbon were significantly (p < 0.001) affected by management (nondisturbed > CT = NT): Resistant organic C was weakly (p < 0.1) affected by management. The structural instability index (change in mean weight diameter between dry-sieved and wet-sieved aggregates) was the only distinguishing the three management regimes among them (nondisturbed < CT > NT). Soil structural instability index was negatively related to total and particulate organic carbon, meanwhile no relation could be established with the resistance organic carbon. Soil bulk density was significantly higher at 0.05-0.15 m than at 0-0.05 m, and it was related with total organic carbon or particulate organic carbon.  Soil infiltration rate varied differently in loamy (NT ≈ CT) than in silty loamy/silty clay loamy (NT << CT) soils, being the only property affected by a highly significant “texture x management” interaction.  Lower infiltration rate values were caused by platy structural forms and elongated horizontal pores in the surface of silty soils.  Soil penetration resistance (0 – 0.05 m) was 0.77 MPa higher in NT than in CT sites, but mean relative compaction values were as low as 84 % in them. Shallow compaction was not a critical concern in NT soils. The number of earthworm individuals was not sensible to detect differences among management regimes. It can be then concluded that no one single soil parameter could describe soil quality in the Rolling Pampa. A previous characterization of topsoil texture is necessary to assess soil quality. The minimum dataset must include structural instability, total or particulate organic carbon, infiltration rate, and penetration resistance (with soil water content control).