Hi, I need help ASAP , I need to solve this PDE(Partial diferential equ) with some constants(integers) unknown that I will later find with NonLinearModelFIt. but I don't understand why the output is the same input with no erros...I really prefer and error to this weird output. Thanks.

DSolveValue[
 {
  Derivative[1, 0][u][n, 
    z] == (Dich4*Derivative[0, 2][u][n, z]) + (kp*Q10^((
      tsoil - tmean)/10)*
      feh*(cplant + cSOM)) - (ko*(u[n, z]/(kch4 + u[n, z]))*(fo2/(
       ko2 + fo2))) + (0.6*(1 - wmax/(1 + (wmax - wo)/(wo)*Exp[-r*n])/
        wmax)*kp*Q10^((tsoil - tmean)/10)*
      feh*(cplant + cSOM)) + ((1 - pox)*kp*Q10^((tsoil - tmean)/10)*
      feh*(cplant + cSOM))
  , Derivative[0, 1][u][n, 0] == 0, u[n, 3] == ch4atm
  }
 , u[n, z]
 , {n, z}, 
 Assumptions -> 
  Element[{Dich4, kp, ko, tsoil, tmean, feh, cplant, cSOM, fo2, kch4, 
    ko2, Q10, wo, wmax, pox, r}, Integers]
 ]