The growth of ratoon rice (
Oryza sativa
L.) is affected by growth of main rice, so it could be evaluated by determining
growing condition of main rice. Objective of the study was to find regression model for predicting ratoon rice growth
rhythm through establishing the quantitative relationship between growth rhythm in ratoon rice and normalized difference
vegetation index (NDVI) after heading of main rice. NDVI at key growth stages of main rice was measured using active
spectrometry for 12 varieties in 2008 and for 23 varieties in 2009, and compared the physiological indexes of main and
ratoon rice. There was an exponential correlation (P < 0.05) between the NDVI after heading of the main rice and biomass,
N concentration of green leaves and stems or leaf area index (LAI) after heading of the ratoon rice for all the 12 varieties in
2008. The regression models from the rice variety experiment in 2008 were used to calculate predicted values with NDVI
after heading of main rice in 2009. The results showed that the predicted values of biomass, N uptake, and LAI in ratoon
rice were significantly different to measured values. However, there were exponential and significantly positive correlation
(p < 0.05) between biomass and N uptake and LAI in ratoon rice and NDVI after heading of main rice in 2009. Therefore,
it suggested that regression models were not perfect, and need to be improved adding more parameters about spectral
characteristic of main and ratoon rice.
