Soil Factors Affecting Molybdenum Uptake by Cauliflower

Molybdenum deficiency of cauliflower (whiptail) has been observed on the acid (pH 4.2 to 5.0) flatwoods soils of Florida. Considerable differences have been noted between cauliflower varieties in their development of molybdenum deficiency symptoms on these soils. Direct applications of molybdenum with and without lime were used as means of correcting the deficiency. Soil and plant analyses indicate that these soils can supply an adequate amount of molybdenum for plant growth by increasing the soil pH. The growing of cauliflower seedlings in acid, heavily fertilized soils limits the molybdenum taken up by the plant. These plants are set in the field in acid soils made even more acid by current fertilization. The plants with low molybdenum content and root systems restricted by transplanting are set in a soil with a low molybdenum supplying power. These conditions result in a temporary molybdenum deficiency in the plants. Subsequently, this deficiency becomes apparent when the damaged buds develop and the whiptailed leaves appear. As the roots grow and the acidity from the fertilizer dissipates, conditions become more favorable for molybdenum uptake by the plants. The degree of bud damage and the subsequent availability of molybdenum to the plants will be major factors in determining the degree of recovery and production of marketable heads by the plants. Failure of the leaves to develop chlorosis is further evidence of the temporary nature of the deficiency. Because molybdenum does not readily leach, there could be a possible danger to livestock if the fields were converted to pastures, following repeated applications of molybdenum for correction of whiptail. The molybdenum supply of the soils is low but probably adequate under favorable soil pH. The safest way to avoid molybdenum deficiency under these conditions is to grow varieties less susceptible to whiptail; to lime soils to as high as is commensurate with other crops grown in the area (pH 5.5 for potatoes); to lime seed beds to pH 6.0 to 6.5; and to use fertilizers containing fewer materials forming temporary acidity, especially in seed beds.