The NLOPTIONS option has nothing to do with your problem. I was referring to using a logit link function and a binomial distribution. This is all straightforward. See the GLIMMIX examples. However, I am now guessing that you have continuous data (biomass) over time. Essentially, the upper asymptote is a parameter, which means that you have a strictly nonlinear model, unless you fix the asymptote at a fixed value. None of the linear or generalized linear procedures will work. You could use NLMIXED, but you will have to learn a bit of programming to code for the main effects and interactions (there is no CLASS statement, and no global tests for interactions and so on). I can't get into all the things you would need to learn. The Schabenberger and Pierce textbook on statistics in the plant sciences shows how to do this (I highly recommend the book). You should also get SAS for Mixed Models, 2nd edition (Littell et al.). You might find the %nlmix macro, fully described in the Littell et al. book, of value for your problem.
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