Uncovering leaf chlorophyll, SPAD, and RGB coherence with the growth of Tatsoi (Brassica rapa subsp. narinosa) under nutrient and water deficiency

The results showed that under extreme nutrient deficiency, yet with optimum watering duration (24 hours), Tatsoi experienced a reduction in leaf SPAD value (56.96%), directly correlated with decreased chlorophyll content (53.97%) and blue (B) value (37.62%). SPAD value was inversely proportional to the red (R) and the green (G) index, with an increase of 36.85% and 34.74%, respectively. The best-fitted model was the multiple linear regression using three variables of RGB color index to predict leaf SPAD value (R2= 0.911) and chlorophyll content (R2= 0.9698). Similar stress characteristics were found to be consistent at different watering durations. However, it was observed that nutrient stress had a more significant effect on Tatsoi growth parameters than water stress. The most affected growth parameter was the plant weight, with an average 85.09% reduction due to the decreasing photosynthesis rate of 23.61% and transpiration rates of 13.23% of all treatments. The correlogram analysis further showed that nutrient solution concentration (TDS) positively correlated with SPAD and chlorophyll content with correlation values of 0.97 and 0.94, respectively. The majority of Tatsoi growth parameters, except for root length, had high correlation values with TDS (> 0.9).