Spillman/Mitscherlich -function

[klps]

Hi

I need to estimate so-called Spillman/Mitscherlich -function to nitrogen wheat response by using Maximum Likelihood Estimation. It takes form Y = m (1-ke^-bx)

where

Y is yield
x is use of nitrogen
m is theoretic maximum yield
k and b are other parameters (I can't explain them properly)

Because the data (x and Y) is divided for several growing seasons and there is also variation in wheat cultivars and in soil separates I need three dummy-variables.

So I need estimates for m, k, b and dummies. And also r^2, f-value for model and standard errors and t-values for parameters.

-kl