Simulation Study On Radiation Use Efficiency Based On Radiative Transfer Process In Rice

Crop canopy morphology directly affects the optical radiation transmission and the radiation distribution inside the canopy, thus affecting the capacity of canopy photosynthetic production and dry matter production capacity. Crop canopy structure is an important factor which has a great impact on the crop dry matter accumulation and economic benefit. Therefore, quantitative analysis and simulation of crop canopy structure and the relationship between radiation transmission, distribution and radiation use efficiency can provide technical support for improving precision of canopy radiation distribution model and the utilization efficiency of light energy, etc. In this study, two kind of rice with different plant type (Oryza sativa L.) were chosen as experimental materials and field experiments were conducted in RuGao in 2012 and 2013, involving two rice cultivars and different nitrogen rates and transplanting density. The results illustrate the spatial and temporal distribution of Rice morphology and different light radiation, build the vertical distribution model of the canopy structure parameters and canopy light radiation with hyperspectral technology, then simulate the quantitative relationship between optical radiation accumulation and photosynthetic production, providing theoretical basis for the accurate quantitative simulation of high yielding cultivation of rice and photosynthetic production.Transplanting density and nitrogen rates has remarkable effect on the size and distribution of rice leaf area index, to some extent, increasing nitrogen rates and transplanting density can improve the total canopy leaf area, the middle leaf area index of canopy is greater than the upper, bottom minimum. The down vertical distribution of accumulation leaf area index of rice canopy conforms with the Logistic equation (R greater than 0.99), and the vertical distribution model of leaf area index was build with hyperspectral technology, the average RRMSE is 17.25%, The simulation effect is better. The spectral spectrum in different bands has different reflectivity, transmittance and interception rate in the rice canopy with in the growth promotion and changes as a single peak (valley), reflectance and transmittance rates reaches a minimum at jointing stage and flowering stage, respectively, the interception rate at flowering stage was maximum. Raising the amount of nitrogen fertilizer and transplanting density can increase rice canopy reflectivity and interception rate, lower canopy transmittance and improve the utilization level of light. Different band optical radiation transmission characteristics have significant differences, but the change trend is similar, the biggest difference is between the green and purple-blue light, the Red light is close to PAR. The transmissivity and transmissivity have significant correlation with downward accumulating LAI. The relationship can be described with an exponential model T=a×e-K×LAI, fitted correlation coefficient R2 is greater than 0.92. As the growth period advance, the average extinction coefficient of rice canopy increased, significant difference was found in different level of extinction coefficient, canopy vertically downward, the extinction coefficient decreases. Extinction coefficient of different wavelengths radiation has significant differences, the size of the order is purple> blue>PAR>red>green light, the difference is greater in the early and later periods.A radiation distribution model of different rice canopy height is build bases on Monsi and Saeki exponential model, with the canopy structural model and the hyperspectral inversion technology. The results show good predictability between simulated and measured values of the model, the average RRMSE of predicted canopy light radiation transmittance is 28.54% and interception is 11.30%. Research on radiation distribution of different light radiation shows that the ratio of purple, blue, green, red transmittance and PAR transmittance is 0.9258,0.9542,1.0315,1.0195, respectively, and R2 more than 0.99.The dry matter accumulation and the accumulation of photosynthetic active radiation of canopy interception along with the change of growth period are analyzed and the model of the rice canopy radiation use efficiency is establish based on the light distribution model of radiate transfer process and hyperspectral remote sensing technology. The results show that change trend of dry matter accumulation and accumulation of intercept photosynthetic active radiation is similar. Slow growth at the early stage of the transplanting, rapid growth of at the jointing stage, the growth rate slowed down at late growth stage. Accumulation of dry matter and intercept photosynthetic active radiation at high nitrogen density is maximum, the second is the low nitrogen high density, high nitrogen and low density, the smallest is low nitrogen and low density. Average radiation energy used efficiency of two rice varieties of different transplanting density and different nitrogen rates have significant differences, the size of the order is N2D1> N1D1> N2D2> N1D2. Radiation use efficiency model was validated with independent field experiment datasets, the average of RRMSE was 25.30%. It shows that the model has better predictability to radiation use efficiency of rice canopy at different growth stages under different environmental conditions. Technical support can be provided for the accurate estimation of crop photosynthesis production and large area full carbon cycle accurate simulation.