Are chlorophylls good indicators of nitrogen and phosphorus levels?¹

Aubergine plants (Solanum melongena cv. Bonica) were grown under controlled greenhouse conditions on a soil substrate supplied with organic fertilizers (15 kg/m2) mixed with calcium sulfate (CaSO4 at 500 g/m2), with different doses of nitrogen (N as N1 = 15, N2 = 22.5, N3 = 30 g/m2) in the form of ammonium nitrate (NH4NO3), and phosphorus (P as P1 = 24, P2 = 36 g/m2) as phosphorus acid H3PO4). Plants were sampled every 15 days, and the pigments chlorophyll a, chlorophyll b, total (a+b) and ratio (a/b), carotene, licopene, and anthocyanins were determined in the leaves. The results showed that increases in rhizosphere N led to increases in foliar concentrations of chlorophyll a and b, both individually and as total chlorophyll, independently of the dose of P applied. Total chlorophyll concentrations were directly correlated with the level of P fertilization. Carotene and licopenes reflected the influence of increasing doses of N, whereas P did not affect these pigments. Anthocyanin levels were affected by both N and P.