nuts.f90 Source File

      subroutine nuts(u1,u2,uu)
      
!!    ~ ~ ~ PURPOSE ~ ~ ~
!!    this function calculates the plant stress factor caused by limited
!!    supply of nitrogen or phosphorus
!!    ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
!!    ~ ~ ~ SUBROUTINES/FUNCTIONS CALLED ~ ~ ~
!!    Intrinsic: Exp

!!    ~ ~ ~ ~ ~ ~ END SPECIFICATIONS ~ ~ ~ ~ ~ ~

      implicit none 

      real, intent (in) :: u1      !kg/ha         |actual amount of element in plant
      real, intent (in) :: u2      !kg/ha         |optimal amount of element in plant
      real, intent (out) :: uu     !none          |fraction of optimal plant growth achieved
                                   !              |where reduction is caused by plant element
                                   !              |deficiency

      uu = 0.

      uu = 200. * (u1 / (u2 + .0001) - .5)

      if (uu <= 0.) then
        uu = 0.
      else
        if (uu < 99.) then
          uu = uu / (uu + Exp(3.535 - .02597 * uu))
        else
          uu = 1.
        endif
      end if

      if (u2 <= 1.e-6) uu = 1.

      return
      end subroutine nuts