Field-Scale Changes in Soil Profile N After 10 Years of Continuous No-Tillage.

A multi-year cropping systems study under no-tillage was initiated in 1999 on a 37-ha field of the WSU Cook Agronomy Farm near Pullman, WA. The study objectives are to: (1) evaluate continuous no-tillage and crop rotation effects on total profile soil nitrogen (N) and (2) relate changes in total soil N to N inputs from fertilizer, N outputs in harvested grain, and field terrain attributes. Soil samples were initially collected in 1999 at 184 geo-referenced locations in a systematic non-aligned grid across the 37-ha field. Soil samples were analyzed for total soil organic N and carbon (C) at 10-cm increments to a depth of 30-cm and then by soil horizon to a depth of 153 cm. 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 collected again in 2008 at the same geo-referenced locations. All N inputs from fertilizer and crops as well as N outputs from harvested crops were monitored at each of the geo-referenced locations. We will present our findings.