Radiation Transfer Characteristics And Radiation Use Efficiency Of Rice

The morphology and canopy structure affects the transfer characteristics of photosynthetically active radiation (PAR) within rice canopy and consequently affects canopy PAR utilization and dry matter accumulation. Analyzing the dynamics of morphology and canopy structure in rice and the effect of morphology and canopy structure on canopy PAR transfer, PAR utilization and grain yield, is very important for high yield production and for improving the simulation precision of canopy light distribution model. Three field experiments were carried out with different cultivars, planting densities and nitrogen rates in rice, and the morphology and canopy structure, characteristics of canopy PAR transfer, dry matter accumulation in aboveground at main growth periods and grain yield at maturity were investigated. The effects of morphology and canopy structure, conditions of incident radiation on characteristics of canopy PAR transfer and PAR utilization, and the relationship between PAR utilization efficiency and grain yield were analyzed. These results help to lay a theoretical foundation for high yield cultivation and simulation in rice crop.The remarkable differences were observed in leaf length, leaf width, leaf area of each leaf under different planting densities and nitrogen rates in rice. Plant hight increased with increasing nitrogen rates. Canopy average leaf inclination decreased gradually from jointing to milking stage. Leaf inclination distribution frequency during 75°-90°increased and that during 0°-45°decreased with increasing planting densities, which caused the increase of average leaf inclination. However, the impact of nitrogen rates on leaf inclination distribution were contrary to planting density. The ratio of leaf area in mid and basal canopy to total leaf area decreased with increasing planting density and nitrogen rate. The trend of cumulative relative leaf area index with relative canopy height was as S shape, which could be described with Logistic equation. The ratio of leaf area in mid and upper canopy to total leaf area increased from jointing to milking stage, and high density and nitrogen rate could accelerate the senescence of leaves in mid and basal canopy. Plant morphology and canopy structure changed significantly with growth progress and were regulated by planting density and nitrogen rate in rice.Dynamics of canopy PAR transmittance and reflectance firstly decreased and then increased with growing progress in rice, and the minimum value appeared around booting to heading stages. Canopy PAR reflectance decreased with increasing nitrogen rate. Extinction coefficient (K) increased over growing progress in rice, and increased with increasing planting density and nitrogen rate. The average values of canopy K over the whole growth periods were close to the values measured at about ten days afte heading stage in two cultivars. The daily change patterns of canopy PAR reflectance and interceptance, and K values changed in downward parabolic curves, reaching the minimum values at noon, while opposite pattern was seen with 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. Daily average K values were close to the values measured at 14:00 during different growth periods. Canopy PAR transmittance decreased and K value increased with decreasing proportion of diffuse radiation. Reflectance and transmittance of canopy blue radiation is higher than that of canopy red and green radiation, while opposite pattern was seen with the interceptance. The difference of transfer characteristics between PAR spectrum was more significant in earily growing stage and late growing stage. The dynamic characteristics of canopy PAR transfer in rice were regulated by planting densities and nitrogen rates, exhibiting remarkable changes over daily times and growth periods, and the extinction coefficient measured at 14:00 about ten days after heading stage could be used for photosynthesis simulation during the whole growth period in rice.Canopy leaf area index (LAI) and leaf area duration of rice were affected significantly by planting densities and nitrogen rates. The average PAR reflectance of different treatments from tillering to maturity was 3.45%, and the canopy reflected PAR from tillering to heading stage was 10.90% of canopy total loss of PAR, which was obviously lower than that from heading to maturity. PAR convertion efficiency from tillering stage to heading stage was significantly higher than that from heading stage to maturity, and which is decreased with increasing planting densities and increased with increasing nitrogen rates from tillering to maturity. PAR use efficiency increased with increasing planting densities and nitrogen rates from tillering to maturity, and the average PAR use efficiency of Liangyoupeijiu was 1.83 g·MJ-1, which was obviously higher than that of Wuxiangjing 14 (1.42 g·MJ-1). Incident PAR and intercepted PAR under middle and high density of Wuxiangjing 14 were higher than that of Liangyoupeijiu, because of the longer growth period of Wuxiangjing 14. There were a significantly positive correlation between PAR interceptance and PAR use efficiency to grain yield, and the nonsignificantly positive correlation was observed between PAR conversion ratio and grain yield. Therefore it is benefit for high grain yield to increase PAR use efficiency by increasing PAR convertion ratio based on high PAR interceptance in rice canopy.