Soil quality under conservation practices on farm operations of the southern semiarid pampas region of Argentina

Abstract Field observations of no-till production plots in the southern semiarid pampas region of Argentina question the sustainability of this practice from the soil quality (SQ) standpoint when the amount of residues left by typical crop rotations is not taken into account. Our aim was to evaluate a set of management practices as they have been implemented on farm operations of the region on SQ parameters of the surface soil. The six production systems identified represent the combinations of tillage systems (no − till, NT and reduced till, RT), time since implementation (10 or 15 years), rotations (WW, winter crops; WF, winter crops with extended fallow; WS, winter and summer crops) and soil types (sandy loam or loam to clay loam) found in the agricultural operations of local producers. Composited soil samples at three successive depths (0–5 cm, 5–10 cm and 10–18 cm) were taken in 27 production plots of ∼50 ha in size each, and analyzed for soil chemical, physical and biological properties. Our results showed when including sunflower as summer crops on the dominant sandy loams, that NT production plots had the lowest total organic carbon (TOC) and total nitrogen (TN), and particulate organic carbon and nitrogen (POC, PN), and showed a three-fold decrease in structural stability when compared with NT of only winter crops or with RT managed plots. Furthermore, our canonical discriminant analysis (CDA) showed structural index (SI), TOC, change in the mean weight diameter of aggregates (CWMD), and biological activity (BA) as the best SQ indicators for the study area. The quantified degradation suggests the need to reassess NT implementation in order to make NT a sustainable option for the southern semiarid pampas region.