Hi!!! im amateur in mathemathicals growth models but im doing my graduated work in adjust five differents models in some growth parameters in onion,

So my doubt is basically in a derivate for gauss model, i cant derivate this model and it had been adjust for some parameters. So i need to know a derivate for continue my growth analysis.

Also, I just dont know if a sentence of that model is right or wrong, same for others models and their derivates. I read some books about nonlinear models and found diferents expressions in Monomolecular, logistic and Richards models, so i put as options (1 and 2). I also have doubt which are right. Finally i didnt understand which values could have parameter M in richards model.

Ill be so grateful with your helps. i'm not physic student, i'm agronomist so you could know better,