Long-Term No-till, Crop Rotation, and Terrain Attribute Effects On Soil Nitrogen.

A multi-year cropping systems study under no-tillage was initiated in 1999 on a 37 ha field of the Cook Agronomy Farm near Pullman, WA. The study objectives are to: (1) evaluate crop rotation and long-term no-tillage effects on changes in total soil nitrogen (N), (2) construct a field-scale mass-balance evaluation of N inputs, outputs, and changes in storage, and (3) relate changes in soil N to soil and terrain attributes. Crop rotations initiated in 2001 consisted of six different three year rotations of spring wheat – winter wheat – alternative crop (spring or winter plantings of barley, canola, lentil, or pea). Soil samples were initially taken at 184 geo-referenced locations in 1999 prior to establishment of no-tillage and crop rotation treatments at 30-cm depth-increments and then by soil horizon to a depth of 153 cm and analyzed for bulk density and total soil organic carbon (C) and N. Samples were collected again in 2008 at the same geo-referenced locations. In 1999, soil N ranged from 0.052 to 0.164 g N kg^-1 in the top 30 cm and 0.0061 to 0.80 g N kg^-1 from 30 cm to 153 cm.  We will present the 2008 data and evaluate the changes in soil N and treatment effects across the 37 ha field.