1. Cate and Nelson (1965)
% yield versus soil test level
Two Groups: 1. probability of response to added fertilizer is small 2. probability of response to added fertilizer is large
A.Percent yield values obtained for a wide range in locations (fertilizer rate studies)
Percent yield = yield at 0 level of a nutrient / yield where all factors are adequate
B. Soil test values obtained (Check Plot)
Will generate a single % yield and one soil test value for each location
C. Scatter diagram, % yield (Y axis) versus soil test level (x axis)
Range in Y = 0 to 100%
D. Overlay
-overlay moved to the point where data in the +/+ quadrants are at a maximum
-point where vertical line crosses the x = critical soil test level

3. Critcal level depends on the extraction method used and crop being grown.
Cate-Nelson: Maximizes the computed chi-square value representing the test of the null hypothesis that the # of observations in each of the four cells (quadrants is equal).

4. 120
100 80
Percent Yield 60 40 20 20 40 60 80
100
120
Soil test P, ug/g