Aspects of the Fe and Mn nutrition of rice plants

Summary In three water-culture experiments, the effects of variations in pH, N form, and Si- and P level on the uptake and translocation of Fe and Mn, and on the chlorophyll contents of lowland rice were examined.It was found that Mn uptake increased with increasing pH, that it was not affected by variations in N form (NO₃ or NH₄), and that Si has a suppressive effect on Mn uptake. With increasing pH, the translocation of Fe to the shoots was reduced. This pH effect might be indirect, in that Fe translocation is hampered by excessive Mn uptake induced by high pH. Variations in N form and in Si level did not influence Fe uptake and- translocation.A combination of high P-and high Mn levels in solution proved to reduce the translocation of Fe to the rice shoots. Precipitation of Mn phosphate on the roots is likely to occur at high concentrations of both Mn and P in the root medium.A negative correlation was found between chlorophyll content and Mn content of the leaves. The chlorophyll content was not related to the iron content of the leaves. It is likely that chlorosis of rice leaves in an early growth stage can be caused by several combinations of the following factors: 1. high Mn supply, 2. NO₃ nutrition inducing an increase in solution pH favouring a further increase in Mn uptake, 3. absence of Si which exerts a suppressive effect on Mn uptake, and 4. high P supply. These factors can induce chlorosis, with and without exerting a concomitant influence on the uptake and translocation of Fe.