Spatiotemporal Assessment of the Late Marginal Heading Date of Rice Using Climate Normal Data in Korea.

Determination of the late marginal heading date (LMHD) would provide information on the potential range of seeding or transplanting dates, which would allow identification of potential double cropping areas and, as a result, establishment of cropping systems. Still, little efforts have been made for determination of the LMHD. The objective of this study was to determine the LMHD in Korea using an objective approach. The LMHD was calculated using accumulated temperature for 40 days. To examine crop productivity on the LMHD, climatic yield potential (CYP) was determined to represent the potential yield under a given climate condition. The value of CYP on a given LMHD was determined using mean temperature and sunshine duration for the same period. Furthermore, the relative yield on the LMHD in comparison with the potential yield was also calculated dividing the CYP value on the LMHD by the maximum value of CYP (CYPmax) in the season of interest. Our results indicated that the LMHD occurred about two days later at most sites under current conditions (1981-2010) than under past conditions (1971-2000). Overall, the minimum value of CYP/CYPmax was 81.8% under all of given conditions. In most cases, the value of CYP/CYPmax was >90%, which suggested that yield could be comparable to the potential yield even though heading would have occurred on the LMHD. When the LMHD could be scheduled later without considerable reduction in yield, the late marginal transplanting date could also be delayed accordingly, which would facilitate double-cropping in many areas in Korea. However, spikelet fertility would be a key factor to determine crop yield, which merits further studies to take into account the sterility on the LMHD along with the temperature conditions during grain filling periods.