Assessment of sunflower water stress using infrared thermometry and computer vision analysis

Abstract

The objectives of the current study were to implement affordable and non-invasive measurements of infrared thermometry, leaf relative water content (RWC), crop water stress index (CWSI), leaf area index (LAI) from computer vision analysis and seed yield of sunflowers. The experiment was designed as split-plot based on randomized complete blocks with three replications. Treatments were four different levels of deficit irrigation as the main plots and three fertilization treatments were applied as sub-plots. Results showed a significant effect (P ≤ 0.01) of water stress and fertilizer on CWSI during different stages of sunflower growth. Changes in fertilizer amount and type resulted in a change in lower (dTLL) and upper (dTUL) limits of canopy-air temperature difference. A combination of chemical fertilizer with biofertilizer could help to decrease CWSI. From computer vision analysis, the normalized difference red blue index (NDRBI) had a strong linear relationship with RWC and CWSI for sunflowers (R2 of 0.87 and 0.93, respectively) and the normalized difference green blue index (NDGBI) had a linear relationship with seed yield (R2 = 0.79). Therefore, analysis of digital RGB images and CWSI were efficient, non-destructive and low-cost methods to assess crop water status for sunflowers under different irrigation and fertilizer treatments. HIGHLIGHTS The CWSI values were sensitive not only to different irrigation regimes but also to amount and type of fertilizer.; The CWSI can be derived from the plant index (NDRBI) and used for appropriate irrigation scheduling.; A positive correlation was observed between image indices with CWSI and LAI.; Combination of chemical fertilizer with biofertilizer could help to decrease CWSI.;

Keywords

• crop water stress index
• digital image processing
• leaf area index
• seed yield
• vegetation indices