c     file: huc1.for

      subroutine huc1 (bctmin, bwtdav, bwtdmn)

c     Author : Amare Retta
c     + + + PURPOSE + + +
c     Calculate heat units and daylength
c
c     + + + KEYWORDS + + +
C     Heat units, daylength
c
c     + + + ARGUMENT DECLARATIONS + + +
      real bctmin, bwtdav, bwtdmn

c     + + + COMMON BLOCKS + + +
c local
*$noereference
      include 'm1flag.inc'
      include 'crop/cenvr.inc'
      include 'crop/cgrow.inc'
*$reference
c
c     + + + LOCAL VARIABLES
      REAL x, sd, pi
c
c     + + + OUTPUT FORMATS + + +
c2000 FORMAT('+',109x,2(F8.2,1X))
c
c     + + + END OF SPECIFICATIONS + + +
c
c     skip daylength calculations if region does not have winter dormancy
c     if (am0drlfl.eq.0) goto 45

c   following print for debugging
c     if (phu.le.0.)goto 95
c     CALCULATE DAYLENGTH
      pi = 3.14159
      hrlty = hrlt
      x = jd-80.25
      sd = 0.4102*sin((2.*pi/365.)*x)
      hrlt = 7.64*acos(-tan(2.*pi*xlat/360.)*tan(sd))
c   following print for debugging
c      write(*,373)bwtdmx,jd,hrlt,hlmn0
c373   format (' bwtdmx=',f6.1,' jd=',i6,' hrlt=',f6.1,' hlmn0=',f6.1)
c     skip heat unit calculations if still in dormancy period
c     and set dormancy flag to 1 or 0

c           am0drlfl = 1
c      if (hrlt .gt. hlmn0) am0drmfl=0
c      if (am0drlfl.eq.1) then
c      start dormancy
        if (drmfl .eq. 1)goto 45
         if (hrlt .le. hlmn0) then
            if (bwtdmn.le.-5.) then
               drmfl = 1
            endif
         endif
 45   continue
      if (hrlt.gt.hlmn0) drmfl=0
      if (drmfl.eq.1) then
         am0drmfl=1
         goto 95
      endif
c     CALCULATE HEAT UNITS
      dhu=bwtdav-bctmin
      if (dhu.lt.0.) dhu=0.
      shu=shu+dhu
      hui=shu/phu

c      WRITE(*,*)'bctmin,bwtdmx,bwtdmn=',bctmin,bwtdmx,bwtdmn
 95   continue
      return
      end