Zinc deficiency in rice
Zinc deficiency of rice is widespread throughout Asia on neutral to alkaline calcareous soils which contain more than 1 percent organic matter. Incidence of the deficiency appears more closely related to zinc availability than to total zinc content of the soil, and spontaneous recoveries of affected crops are common.
Results of the present study indicate that transient peaks in the concentration of bicarbonate and possibly of organic acids in the soil solution following soil submergence may induce temporary zinc deficiencies. In laboratory experiments with a known problem soil, bicarbonate concentration reached a peak of 42 mM 5 weeks after soil submergence, and the concentration of organic acids peaked at approximately 10 me/l after 4 weeks. Addition of cellulose to the soil raised bicarbonate concentrations substantially and organic acid concentrations slightly.
Solution culture studies with the variety IR8 showed that with a bicarbonate concentration of only 15 mM, transport of zinc to the shoots was reduced by more than 70 per cent. Under neutral to alkaline conditions, acetic acid at 10 me/l produced only slight reductions in zinc uptake and transport to the shoots. However at pH 4.5 the same concentrations of acetic acid reduced uptake by more than 90 per cent.
Delaying planting for 12 weeks after soil submergence to allow bicarbonate (and organic acid) concentrations to fall increased zinc uptake from three soils by from 53 to 84 per cent.