Interactions with Phosphorus and Sulfur

The molybdenum nutrition of plants can be affected by the interaction of molybdenum with other nutrients in the soil such as phosphorus and sulfur. It is well established that plant uptake of molybdenum is enhanced by the presence of soluble phosphorus and decreased by the presence of available sulfur (87). In comparison to MoO₄^2-, phosphate has a greater affinity for sorption sites in soils, such as on sesquioxides (92). Phosphorus fertilization often liberates soil-bound molybdenum into the soil solution and increases molybdenum accumulation by plants (85,97). Phosphorus may also stimulate molybdenum absorption through the formation of a phosphomolybdate complex in soils, which may be readily absorbed by plants (98). The effect of sulfur on molybdenum absorption by plants appears to be related to the direct competition between SO₄^2- and MoO₄^2- during root absorption. Stout and Meagher (99) showed that the addition of SO₄^2- to the culture medium reduced absorption of radioactive molybdenum by tomatoes, and decreased molybdenum absorption by tomatoes (Lycopersicon esculentum Mill.) and peas (Pisum sativum L.) in soil (100).