title: Argentinean Pampa soil 16S pyrotags
description: Soil samples were collected between June and August 2010 at two different locations in Argentine Pampas. Sampling was done in production fields and in experimental plots. Production plots were sampled in three different farms located in the Rolling Pampas: La Estrella, La Negrita and Criadero Klein.   Rolling Pampas Soils are classified as Typic Argiudolls (USDA 1975) and mean annual precipitation and temperature are 1002 mm and 16.8 ºC. Production soils were under agricultural management for at least one century, with a mixed rotation of pastures and annual grain crops during the first decades and only grain crops for the last 30 years. Soils were managed under no-till for the last 10-15 years. The last crop rotation was wheat-soybean. Nitrogen fertilization was performed. Samples were collected a month after soybean harvest on June 2010. Soil samples were also collected nearby the farmers’ houses where no land use has been recorded in the last 30 years except from grass mowing. Parks around farmers' houses are usually considered as undisturbed (i.e. no land use) environments in Argentine Pampas (Vazquez et al. 1990). Soils under no land use were covered with grass and other herbaceous (non-woody) plants common in the region such as Cirsium sp, Trifolium sp, Micropsis sp, Festuca sp, Dichondra sp, Cyperus sp and Taraxacum officinale. Soil cores were taken with an auger from the upper 20 cm soil layer, from 20 randomly selected locations within an area of ~500 m2 in each plot. Cores were then pooled together.   The second sampling location was a 34 year- crop rotation experiment located in Balcarce in the Southern Pampas. Soils in Balcarce are classified as a complex of Typic Argiudolls and Petrocalcic Paleudols and mean annual precipitation and temperatures are 875 mm and 13.8 ºC. The experiment was carried out as a randomized complete block design with a split-plot treatment arrangement, three replicates, and 10 by 35 m experimental units. Treatments assigned to main plots were referred to as no-till or conventional tillage (under mouldboard plough). Rotations have included pastures and grain crops during the last 16 years. Nitrogen fertilization was performed (90 kg N ha-1). Last rotation before sampling was corn-soybean. Samples were collected from all treatments and replicates on August 2010, a month after soybean harvest. Soil samples were also taken in triplicate nearby the farm houses where no land use has been recorded in the last 30 years except from grass mowing. This area was covered with grass and other herbaceous (non-woody) plants common in the region. Samples were collected as in Rolling Pampa. Composite samples were immediately sent to the lab where they were air dried for 2/3 days and sieved through 1 mm mesh to thoroughly homogenize, break aggregates and remove roots and plant detritus. Samples were then stored at -80 °C.  DNA was isolated from 10 g of soil using the PowerMaxSoil DNA Isolation Kit following the manufacturer’s instructions (MO BIO Laboratories, Inc, CA, USA). Technical replicates were defined by performing up to 4 independent extractions per sample. A total of 42 DNA samples were used. The V4 hyper variable region of the 16s rRNA gene was amplified in duplicate PCR reactions using 520F and 802R bacterial universal primers. Amplicons were pooled and equimolar concentrations pyrosequenced at INDEAR (Argentina). on a Roche FLX 454 pyrosequencer running the Titanium chemistry