Abstract:

The study was carried out to investigate the effects of different row directions on use-efficiency of solar radiation in canopy bottom and rice yield for improving the utilization of light resource. ‘Nanjing 9108’ was cultivated with three row directions according to the geographical latitude and solar altitude angle as local conventional north-south direction, that was magnetic south 0^o (CK), 30^o from southeast (SE30), and 30^o from southwest (SW30). Solar radiation intensity and photosynthetic parameters from canopy bottom were analyzed at filling stage; aboveground biomass and yield were measured at harvest. The results showed that adjusting row direction had a significantly effect on the total solar radiation intensity at the leaves of canopy bottom, which was in the order of SE30<SW30<CK from 8:00 to 17:00. The peak solar-radiation intensity on the leaves of canopy bottom in SE30 treatment was advanced to 11:00, while the higher solar radiation intensity of SW30 treatment maintained from 12:00 to 16:00. Due to the higher total radiation intensity and the longer duration of higher radiation intensity, the photosynthetic rate, transpiration rate and stomatal conductance of rice leaves in SW30 treatment were increased by 17.3%, 28.0% and 34.0% than those in CK, respectively. However, these properties of SE30 treatment were reduced by 9.9%, 10.3% and 26.0%, accordingly. After harvest, compared to CK treatment, SW30 treatment significantly increased both aboveground biomass and yield (approximate10.0%). The SE30 treatment had no significant impact on biomass, but the yield of which was decreased by 3.5%. Finally, SW30 treatment had the highest solar radiation use-efficiency on leaves of canopy bottom, which were 11.2% and 12.4% higher than those of CK and SE30, respectively. All these indicate that the adjustment of rice row direction to 30^o southwest can significantly improve the solar radiation use-efficiency of leaves located in canopy bottom, thereby promotes biomass accumulation and yield formation. Thus, adjusting rice planting direction might be a potential way to improve rice production without increasing economic input in Jiangsu Province.

Key words: row direction, solar radiation, photosynthetic parameters, biomass, yield