| This investigation established the monitoring model of wheat plants water content based on the visible light transmission derivative parameters, which aimed to provide a technical reference for the rapid and non-destructive monitoring of crop water condition and the accurate management of field irrigation. In this study, three-year field experiments were conducted to determine the canopy transmission spectrum and plant water content at different growing stages of wheat, and the quantitative relationship between the first derivative of transmission spectrum and plant water content were established. The results showed that the first derivative parameters reduced the influence of the growth stage well compared with the original transmittance. Combining dataset from different growth stages, the correlation between transmittance and plant water content at all respective bands was worse,and the first derivative had a strong correlation with the plant water content at 439 nm, 735 nm, 823 nm and 950 nm(|r|>0.57), among which the correlation was strongest at 735 nm. Based on the characteristics and combinations of blue, yellow and red light bands, 21 spectral parameters were selected. Among them, red edge amplitude(Dr), red-blue amplitude normalization index(Dr-Db)/(Dr+Db), red edge area(SDr), right peak area(RSDR), double-peak area ratio(RIDA) and double-peak area normalization index(NDDA) have better correlation with plant water content(r>0.70). The regression analysis between the above optimized parameters and plant water content showed that RIDA and NDDA were the best. The fitting accuracy r was more than 0.69, and the root mean square error(RMSE) was lower than 4.87, which showed the models had good stability, can estimate the wheat plant water content. The results indicated that the canopy derivative transmission spectroscopy can be used to monitor the wheat plants water content, which has great application potential in guiding the management of crop precision irrigation. |
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