A comparison of the methods used to assess the nutritional status of selected crop species

Various devices and applications are used for the rapid assessment of plant nitrogen nutrition, which give an approximate indication of leaf chlorophyll saturation by giving the relative chlorophyll content or leaf greenness intensity. In this study, chlorophyll content and leaf greenness determined by three devices were compared: SPAD-502 (spectrum technology), Hydro N-Tester, and Samsung smartphone (RGB app). Additionally, laboratory determination of chlorophyll content was compared to soil-plant analysis development (SPAD) values. Based on the results obtained, indices characterising the vegetative or direct state were calculated and the values obtained with these devices were compared. The crops tested were soya, potatoes, wheat and sunflower. The results show a close relationship between the size of the SPAD index and RGB light sources of colour the intensity of red (R), green (G) and blue (B). The indices IPCA and R+G–2B showed a very high negative correlation with SPAD readings (−0.82 and −0.83). Statistical analysis showed that SPAD readings obtained from the two chlorophyll meters showed a high correlation regardless of the crop species tested (R2 = 0.98). The correlation analysis also showed the possibility of substituting equipment and vegetation indices based on readings taken with a smartphone, with an accuracy not much inferior to standard chlorophyll meters. This situation could occur in case of failure or absence of the standard device.