Detection potential of maize pollen release stage by using vegetation indices and red edge obtained from canopy reflectance in visible and NIR region

摘要

Monitoring pollen release is important for investigating growth stages and pollen dynamics of agro-ecosystems. The objective of this study is to evaluate the possibility of using four vegetation indices (normalized difference vegetation index, NDVI; optimized soil-adjusted vegetation index, OSAVI; photochemical reflectance index, PRI; and, water band index, WBI) and the red edge to relate tassel condition and pollen release number during the maize flowering season by non-destructive optical observation of hyperspectral reflectance. Canopy reflectance of the maize crop was measured by a spectroradiometer within the spectral range of 300-1100 nm. A Durham sampler was used to collect the pollen. The results showed that the pollen number increased rapidly from the onset of the pollen release and then decreased slowly until the tassel withered. The OSAVI and PRI decreased most conspicuously after the maize began pollen dispersal. The temporal difference of the vegetation index, particularly that of OSAVI, also corresponded to the change in pollen release. The correlation between the vegetation index of the first derivative of the reflectance spectra at the red edge and the 2-day average pollen amount (August 5 to 14) was detected by correlation analysis (R-2=0.26 for NDV1; 0.72 for OSAVI; 0.68 for PRI; 0.56 for WBI and 0.85 for the first derivative at the red edge position). Therefore, the first derivative of the reflectance spectra at the red edge position allowed prediction of the onset and peak of pollen release, which are promising for assessing the potential for pollen contamination.