Cate and Nelson (1965)

% yield versus soil test level

Two Groups:1. probability of response to added fertilizer is small2. 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

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Critical Level

Perc

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Soil Analysis, ppm P

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).

Quadratic CL = 92Linear Plateau = 52

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