Zinc deficiency in fields of flooded and upland rice have been reported from India O. 2). West Pakistan (2), Japan (3, 4, 5), U. S. A. (6). and Brazil (Sousa de, D. M. and Hiroce, R.. personal communication). These reports indicate that zinc deficiency in rice is prevalent in soils ranging from about neutral to alkaline. and, in particular, in calcareous soils. Since much of the Philippines is derived from lime-!lionel! and coral reefs. zinc deficiency of rice ought to occur in the Philippines. In a survey of nutritional disorders of rice in March-1969, we observed a severe disorder of rice on the island of Cebu. The symptoms of this disorder, known locally as "Taya-Taya," were similar to the symptoms of zinc deficiency (2). Chemical analyses and greenhouse and field experiments have subsequently established that the disorder "Taya-Taya" is zinc deficiency. A survey in March 1970 on the east coast of ubu island confirmed that zinc deficiency was widespread in the area. In the same year. we fuund another example of zinc deficiency of rice on a neutral soil in southern Luzon. Materials and Methods A. 1";eld observations and chemical analyses 0/ plant and soil samples.

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Zinc deficiency occurs widely in lowland rice in Asia. The incidence of zinc deficiency is correlated positively Y{ith high pH, low available zinc content, and high organic matter in the soil. The problem fields often have poor drainage. An example of zinc deficiency was recorded for a "normal field" that had been cropped continuously. Visible symptoms and plant analyses were used as diagnostic tech• niques. The application of zinc sulfate, zinc chloride, zinc oxide, and FTE to the soil, and dipping roots of seedlings in 1 or 2% zinc oxide suspension were quite effective. Merits and shortcomings of these methods are discussed.

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Solution culture studies revealed no marked difference in the ability of the resistant variety I R 8 or the susceptible variety IR184-67 to absorb zinc from low external concentrations comparable with those occurring in the soil solutions of deficient soils. H o w e v e r I R 8 appeared to have a slightly lower tissue requirement for zinc than IR184-67 (critical values 0.23 and 0.27 lag atoms/g respectively) and IR8 was significantly less susceptible to bicarbonate concentrations ( < 1 mM). Despite these differences, the two varieties appeared equally susceptible to zinc deficiency during the first four weeks of growth under field conditions. I n the field, both varieties underwent a spontaneous recovery from zinc deficiency after four to eight weeks' growth, but the recovery of I R 8 was more rapid and more complete in terms of both shoot growth and final grain yield t h a n t h a t of IR184~57. The superior ability of I R 8 to recover from an initial set-back due to zinc deficiency was further demonstrated in a solution culture experiment. I t is concluded t h a t differences in the field performance of the two varieties under conditions of zinc deficiency are largely due to differences in ability to recover when zinc again becomes available to the plant.