Introduction

The observation that molybdenum (Mo) uptake by plants decreases with increasing concentrations of sulfate was first reported for tomato plants (Lycopersicon esculentum Mill.) in solution culture (Stout and Meagher, 1948). Stout et al. (1951) confirmed that observation with tomato plants grown in tissue culture (Table 14.1) and with tomatoes and peas (Pisum sativum L.) in soil (Tables 14.2 and 14.3). They attributed the action of sulfate ions in suppressing Mo uptake to direct competition between two divalent anions of similar sizes.

Since the report by Stout and co-workers, the effects of sulfur (S) to decrease Mo uptake have been reported in many species grown under a wide range of conditions, including vegetable crops such as beans (Phaseolus vulgaris L.) (Widdowson, 1966), Brussels sprouts (Brassica oleracea L. Gemmifera Group) (Gupta and Cutcliffe, 1968; Gupta, 1969; Gupta and Munro, 1969), cauliflower (Brassica oleracea L. Botrytis Group) (Mulder, 1954), cauliflower and lettuce (Lactuca sativa L.) (Plant, 1956), peas (Reisenauer, 1963; Gupta and Gupta, 1972), and peas and tomatoes (Stout et al. 1951). Similar relations between Mo and S have been found in forages such as berseem (Trifolium alexandrinum L.) (Pasricha and Randhawa, 1972; Shukla and Pathak, 1973; Sisodia, Sawarkar, and Rai, 1975; Pasricha et al., 1977;