Phosphorus and molybdenum interaction effects during accumulation of molybdenum by burley tobacco 1

Greenhouse experiments were conducted to study the P and Mo interactions during uptake by burley tobacco (Nicotiana tabacum L., cv. ‘Ky 14') and the effect of their interactions on plant dry matter and Mo concentration. In Experiment 1, plants were grown in an intermittently irrigated gravel culture system. The nutrient variables were Mo (0–0.63 μeq/L) and P (0 to 1.8 meq/L). Experiment 2 was conducted in soil‐sand mixtures. The soil types used were Shelbyville silt loam (Mollic Hapludalf) and Baxter silt loam (Typic Paleudalf) each containing, respectively, 36 and 368 kg P/ha by the Bray 1 soil test. Treatments consisted of four rates of P (0, 84, 168, and 336 kg/ha) and five rates of Na₂MoO₄‐2H₂O (0, 0.56, 1.12, 2.24, and 4.48 kg Mo/ha).

In gravel culture a significant synergistic Mo × P interaction occurred for dry weight, but singly the effect of P was greater than Mo. Similarly, significant positive Mo × P interactions occurred for Mo concentrations in both gravel and soil culture. As contrasted to adding no P or Mo, adding the highest levels of P and Mo together increased Mo concentrations in leaves four, five, and 10 fold, respectively, in gravel culture, Shelbyville, and Baxter soils. The rate of accumulation of Mo was much greater at plant Mo concentrations above 1 μg Mo/g tissue than below, suggesting two mechanisms of Mo × P interaction were involved.