Transfer Characteristics of Canopy Photo-Synthetically Active Radiation in Different Rice Cultivars Under Different Cultural Conditions

【Objective】 The objective of this study was to explore the dynamic transfer characteristics of canopy photosynthetically active radiation(PAR) in different rice cultivars and under different cultural conditions.【Method】Field experiments were conducted in Nanjing in 2009 and in Yizheng in 2010,involving two cultivars with different plant types,three planting densities and five nitrogen rates.During rice growing periods,the dynamics of canopy structure and the daily changes in PAR transfer parameters were measured,and the effects of proportion of diffuse radiation on canopy PAR transfer characteristics were analyzed.【Result】 The results indicated that canopy leaf area index(LAI),average leaf inclination and plant height of rice were affected significantly by planting densities and nitrogen rates.Dynamics of canopy PAR transmittance and reflectance firstly decreased and then increased over growing progress of rice,with the minimum value appeared during booting to heading stages.Canopy PAR reflectance decreased with enhancing nitrogen rates.Extinction coefficient(K) in canopy increased over growing progress of rice and with increasing planting densities and nitrogen rates.The dynamics of K with the days after transplanting could be described with the upward exponential equation.The daily change patterns of canopy PAR reflectance and interceptance,and K values could be described with downward parabolic curves,reaching the minimum values at noon,while opposite patterns were seen in the PAR transmittance.The ranges of daily variation in canopy PAR transmittance and interceptance,and K values at grain filling stage were obviously lower than those at tillering stage.The dynamics of K with the solar angle could be described with the Doseresp curve,which was affected by the canopy structure and cultivar genetic characteristics.Canopy PAR transmittance decreased and K value enhanced with reduced proportion of diffuse radiation.【Conclusion】The dynamic characteristics of canopy PAR transfer in rice were regulated by planting densities and nitrogen rates,exhibiting marked changes over daily times and growth stages,and affected by the proportion of diffuse radiation.These results will provide experimental supports for precision simulation of canopy photosynthesis and productivity in rice.