Linking a Decade of Geospatial Information and Alternative Land-Use Management to Soil Quality.

The Palouse region of the Pacific Northwest contains some of the most highly erodible soils in the United State. Long-term continuous direct seeding, a form of no-till and alternative crop rotations have been shown to improve soil quality. This study incorporates soil quality measurements and geospatial information collected annually for 10 yr at geo reference sites across landscapes and rotations under direct seed. Twelve-ha field plots were divided into landscape positions: summits and south slopes with a Bt horizon (SSw/Bt), summits and south slopes without a Bt horizon (SSw/oBt), north slopes and bottoms with a Bt horizon (NBw/Bt) and north slopes without a Bt horizon (NSw/oBt). Soil samples were collected in spring wheat entry points of winter wheat-chickpea-spring wheat and winter wheat-barley-spring wheat rotations. Soil quality measures were employed to determine the affect of 10 yr of land-use on plant available N, particulate organic matter (POM) and the size and turnover rate of organic N pools. Nitrifcation potentials, inorganic N (NH₄ ⁺ + NO₃^-)-N and POM nitrogen reflected shifts in seasonal nitrogen availability due to rotation and landscape position. Inorganic N measurements were significantly higher in SS than NS positions (41 vs. 28 mg N kg^-1 soil) and in legume rotations (42 vs. 27 mg N kg^-1 soil). Nitrification potentials and POM-N were significantly higher in summit south slope*legume rotations. POM-C revealed increases in C on all landscape positions and rotations due to long-term direct seeding. Nitrogen pools were significantly higher in the legume rotation of the SSw/Bt (244) relative to the small grain rotation of the NSw/oBt (97.1 mg N kg^-1 soil). Larger pools of soil N contributed to increases in seasonal plant available N. These results indicate that land-use management, alternative crop rotations and geospatial information can be coupled to verify and improve soil quality.