Nutrient Management Research Database

http://ucanr.edu/sites/nm/files/76600.pdf

The status of potassium (K) and phosphorus (P) nutrient concentrations in the Western U.S. soils was evaluated from a survey of analytical laboratories. Over half of the samples analyzed were medium or lower in P, while the concentrations of soil K ranged from 3% medium or lower in NV to 44% medium or lower in CA. Analysis of crop nutrient removal rates compared with fertilizer and manure additions indicate that may soils are currently declining in fertility, a trend that is not sustainable for maintenance of high yields.

• This 2001 survey of over 60 private and public testing labs sought to evaluate the potassium and phosphorus status of soils across the United States.
• A total of 2.5 million individual soil samples was represented in this survey.
• The results of the soil tests were compared with current fertilizer application trends and crop removal rates for the western United States.

• A total of 47% of California soil P tests indicated medium to low levels.
• For potassium, 44% of the California samples had medium to low test results.
• While these results reflect broad trends, and cannot be used to make field specific recommendations, they suggest that many operations require P and K fertilization to maintain high yields.