The study aims to establish relationship between spectral reflectance of rice canopy, crop growth, chlorophyll concentrations and water use. Two fields were chosen for radiometric and agronomic measurements over the period from flowering to maturity (August to November).
A hand held radiometer (model 100 BX) was used to measure spectral reflectance with four bands corresponding to 1, 2, 3 and 4 of the multi-spectral scanner on board Landsat 4 and 5. A high value of spectral response is observed for crop at water level because of multiple scattering effects between crop canopy and smooth water surface and low response is observed when rice plant is way above the water level.
The results indicate that when periodic spectral measurements are available throughout most of the growing season, crop growth and chlorophyll can be monitored well and good prediction of yield can be made during heading stage (66 to 70 days after planting).
Based on the results obtained from the field on spectral measurements of rice plant canopies, it can be concluded that, there was a positive linear relationship between band 1 reflectance and days after planting (DAP) throughout the measurement period (56 to 106 DAP). Band 2 and 3 reflectance values were negatively related to DAP until the flowering phase (68 DAP) and positively related to DAP during senescence of the crop. Infrared band 4 was inversely related to DAP after panicle stage.
The rice plant canopy shows high chlorophyll ‘a’ concentration during early growth (vegetative and early reproductive stage), which decreased during the flowering and maturity stages when the plant attains its maximum height (92 cms).
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