The POM fraction represents a slowly available reserve of soil nutrients such as N and P which may be released during the growing season and replenished from seasonal surface residue. Soil organic matter, particulate organic matter carbon, and total soil N at all sites. Graphs are arranged according to annual precipitation. Touchet receives 7-9 inches of rainfall and Palouse receives approximately 22 inches. Soil pH was as low as 4.6 at the Touchet site and 4.9 at Palouse.
Ammonium based fertilizers acidify soil pH through the process of nitrification to nitrate.
Since the NT drills used at these sites places the fertilizer roughly in this zone, the pH effect may reflect the local area of fertilizer placement. At most sites, the higher P levels were evident to a depth of 10 inches. The three growers at these sites use the Yielder drill and routinely band starter P. Soil K was statistically higher at three sites and likely reflects the placement of K fertilizer. While some relationships between soil test P, soil pH, and soil organic matter might be possible, the higher levels of P under NT at three of the sites and the higher P value for CT at Lewiston, likely represent differences in fertilizer management between growers. Soil pH, phosphate-P, and microbial biomass C at six sites.