real function plant_wat_t( begind, endd, thetaf, thetaw,
     &                           bszlyt, nlay )

      integer nlay
      real thetaf(nlay), thetaw(nlay), bszlyt(nlay)
      real begind, endd

      integer lay
      real sum, depth, prevdepth, temp, thick

      sum = 0.0
      depth = 0.0
      prevdepth = 0.0
      do lay = 1,nlay
          depth = depth + bszlyt(lay)
          if(         (depth .gt. begind)
     &       .and. (prevdepth .lt. endd) ) then
              if(  prevdepth .le. begind
     &            .and. depth .ge. endd ) then
                  thick = endd - begind
              else if( prevdepth .le. begind ) then
                  thick = depth - begind
              else if( depth .ge. endd ) then
                  thick = endd - prevdepth
              else
                  thick = bszlyt(lay)
              end if
              sum = sum + (thetaf(lay) - thetaw(lay)) * thick
          end if
          prevdepth = depth
      end do
      plant_wat_t = sum

      return
      end