Correlation Between Soil Test Values and Plant Nutrient Concentrations.

The purpose of this research is to examine the relationship between soil test values for phosphorus (P) and plant tissue concentrations of P in soybean.  A survey of 65 farmers’ fields throughout Ohio was conducted in 2013.  Three areas were identified in each field to collect samples from according to historical yields:  two normal-yielding areas and one low yielding area.  Soil samples were collected in spring and soil test P was determined using a Mehlich-3 extractant. Leaf tissue samples were collected during the R1 reproductive stage and analyzed for P concentration.  Soil P levels and plant tissue P levels were compared and referenced against existing nutrient recommendations based on soil and plant analysis. Preliminary results show that there was a poor correlation between soil test values and plant tissue concentration. Factors that were suspected causes of this poor correlation were also analyzed and included soil-test P, pH, soil texture, and soybean cyst nematode. A multiple regression analysis showed that none of these factors on their own or in combination caused a statistically significant impact on the correlation between soil-test P and leaf P concentration. These results imply other factors that were not analyzed are impacting the correlation between soil-test P and leaf P concentration. Also, current P fertility recommendations for Ohio may need to be reevaluated to improve fertilization practices.