Agricultural producers in the Palouse region of the inland Pacific Northwest have expressed concern over declining soil health, specifically soil acidification, compaction, and declining soil organic matter. These producers seek field-scale monitoring tools and evaluation of innovative and alternative farm management practices to improve soil health and restore soil ecosystem function. This project aims to 1) evaluate the impact of management practices on select soil health indicators, and 2) identify soil monitoring tools and methods that are rapid and relevant to on-farm agroecosystem decision making. Soil physical properties of bulk density, penetration resistance, and single ring infiltration were measured in the spring of 2016 on multiple fields within five farms, totaling 15 field sites. Two locations within field sites were designated for monitoring. Each physical property measurement was replicated three or more times at the two locations and averaged to assess variability associated with the different monitoring tools. Land use at these sites include pasture management, no-till crop production, cover crop integration, and mixed perennial-annual crop rotations. Microbial respiration (Solvita CO2burst), soil organic matter (loss on ignition), and pH were also measured at these sites to relate soil physical properties to soil biological and chemical properties.
Preliminary results indicate an observable positive relationship between bulk density and penetration resistance (PR). This suggest that PR could be calibrated to provide a more practical in-field measurement for rapid on-farm monitoring and evaluation of management practice impacts on compacted layers within the soil profile. Penetration resistance values ranged between 193 – 1856 kPa in the top 7.5 cm of soil across all field sites. Values of PR >2000 kPa are generally considered to be limiting to root growth, and were observed at 46% of all monitoring sites at soil depths below 7.5 cm. Infiltration rates were highly variable across all sites, with an average of 36 cm hr-1 (27 s.d.) and range of 1 – 95 cm hr-1. The influence of soil moisture on the relationship between bulk density and PR measurement values will be included in analysis and a second year of monitoring will be completed to verify preliminary conclusions. Additionally, correlation of soil physical properties to other important soil ecosystem characteristics will be analyzed to work towards determining thresholds of concern, or critical limits, of soil physical measurements for the Palouse region. Interpretation of results for applicability to farm management and implications to soil ecosystem function will be discussed.