RESUMO
On a P-poor, calcareous soil, three upland cotton (Gossypium hirsutum L.) cultivars (ST 402, ST 405, Zeta 2) were tested for 2years under three P rates (0, 13.1, 26.2kgPha-1 ). Leaf traits (SPAD values; specific leaf area, SLA; carbon isotope discrimination, Δ; 15 N natural abundance, δ15 N) and elements (N, P, K, C, Na, Zn) along with arbuscular mycorrhizal (AM) colonisation were measured at first open flower, full bloom and first open boll stages. Phosphorus addition decreased yield, but had no effect on fibre quality, a response attributed to P-induced Zn deficiency, previously reported for cereals. The best-performing cv., ST 405, had high SPAD and SLA, but the lowest P, N and Zn concentrations, an indication of cultivar's high use efficiency for these nutrients. At full bloom, SPAD was lowest, while SLA was highest. AM increased gradually with growth stages, while N, P, K and Zn concentrations showed an opposite trend, possibly due to a dilution effect. On Mediterranean calcareous soils, P fertilisation should take into account soil Zn levels in order to avoid P-Zn antagonistic relationships, which could impact negatively on yield.