In 1938, the importance of molybdenum (Mo) for crop plants was established by Arnon and Stout working with tomatoes in water culture or solution culture (Marschner 1995; Fageria, Baligar, and Jones 2011). The Mo-deficient tomato plants developed mottling of the leaves and evolution of the laminae, showing that some specific metabolic processes in the plant had been affected by the deficiency. Since then, in some regions, spectacular increases in crop growth have been obtained with Mo fertilization, and every year new areas benefit from Mo. Upland rice plant response to Mo fertilization applied to Brazilian Oxisol has been observed (Figure 12.1). Similarly, lowland rice grown on Brazilian Inceptisol also responded to Mo fertilization (Figure 12.2). In India, Subba Rao and Adinarayana (1995) reported an average grain yield response of 130-880 kg ha−1 (5-35%) for rice grown in different soils to which Mo had been applied. Anderson (1956) reviewed literature on Mo fertilizer and reported the marked response of subterranean clover (Trifolium subterraneum L.) and alfalfa (Medicago sativa L.) to Mo in Australia. The commercial use of Mo on nearby deficient pastures followed almost immediately (Anderson 1956). Graham (2008) reported that 15% of the world’s soils are Mo deficient. Similarly, among 190 soils worldwide, it was reported that 3% had an acute Mo deficiency and 12% had a latent deficiency (Sillanpaa 1982). Zou et al. (2008) reported that about 47% of the agricultural land in China, mainly in the east, is Mo deficient.