Carbonaceous aerosols in PM10 and pollution gases in winter in Beijing

IEECAS SKLLQG

Characterization and source apportionment of atmospheric organic and elemental carbon during fall and winter of 2003 in Xi'an, China

IEECAS SKLLQG

Use of Zr/Rb ratios in Chinese loess sequences to trace paleo-winter monsoon winds strength

IEECAS SKLLQG

Radiation-use efficiency and the harvest index of winter wheat at different nitrogen levels and their relationships to canopy spectral reflectance

Radiation-use efficiency (RUE, g/MJ) and the harvest index (HI, unitless) are two helpful characteristics in interpreting crop response to environmental and climatic changes. They are also increasingly important for accurate crop yield simulation, but they are affected by various environmental factors. In this study, the RUE and HI of winter wheat and their relationships to canopy spectral reflectance were investigated based on the massive field measurements of five nitrogen (N) treatments. Crop production can be separated into light interception and RUE. The results indicated that during a long period of slow growth from emergence to regreening, the effect of N on crop production mainly showed up in an increased light interception by the canopy. During the period of rapid growth from regreening to maturity, it was present in both light interception and RUE. The temporal variations of RUEAPAR (aboveground biomass produced per unit of photosynthetically active radiation absorbed by the canopy) during the period from regreening to maturity had different patterns corresponding to the N deficiency, N adequacy and N-excess conditions. Moreover, significant relationships were found between the RUEAPAR and the accumulative normalised difference vegetation index (NDVI) in the integrated season (R-2 = 0.68), between the HI and the accumulative NDVI after anthesis (R-2 = 0.89), and between the RUEgrain (ratio of grain yield to the total amount of photosynthetically active radiation absorbed by the canopy) and the accumulative NDVI of the whole season (R-2 = 0.89) and that after anthesis (R-2 = 0.94). It suggested that canopy spectral reflectance has the potential to reveal the spatial information of the RUEAPAR, HI and RUEgrain. It is hoped that this information will be useful in improving the accuracy of crop yield simulation in large areas.

Spectral response of winter wheat to crop development and various agronomic limitations

For maximizing the effective applications of remote sensing in crop recognition, crop performance assessment and canopy variables estimation at large areas, it is essential to fully understand the spectral response of canopy to crop development and varying growing conditions. In this paper, the spectral properties of winter wheat canopy under different growth stages and different agronomic conditions were investigated at the field level based on reflectance measurements. It was proved that crop growth and development, nitrogen fertilization rates, nutrient deficit (e.g. lacking any kind of nitrogen, phosphorus and kalium fertilizer or lacking all of them), irrigation frequency and plant density had direct influence on canopy reflectance in 400-900 nm which including the visible/near infrared bands, and resulted in great changes of spectral curves. It was suggested that spectral reflectance of crop canopy can well reflect the growth and development of crop and the impacts from various factors, and was feasible to provide vital information for crop monitoring and assessment. ©2010 IEEE.