Role of the rhizosphere in utilization of inorganic iron‐III‐compounds by corn plants

Using a nutrient solution with nitrate‐nitrogen, a strong interaction between iron and phosphorus uptake in water culture was observed. Iron chlorosis could be prevented only by a very high supply of iron‐III‐hydroxide or a very low supply of phosphorus, both of which resulted in a normal chlorophyll content but produced plants deficient in phosphorus. However when iron and phosphorus were supplied to separate root zones (split‐root technique), iron‐III‐hydroxide was a satisfactory source of iron for corn plants even in water culture. In contrast to corn plants grown in water culture, plants in sand culture (quartz sand) with the same nutrient solution utilized iron‐III‐hydroxide just as well as iron chelate, even when high phosphorus concentrations were simultaneously present. Using 59 Fe and circulating the nutrient solution through the sand culture, it could be demonstrated that the mobilization of iron from iron‐III‐hydroxide is restricted to the root‐sand (iron‐III‐hydroxide) interface (rhizosphere) without increasing the amount of soluble iron in the bulk substrate. The depletion of phosphorus around the roots in sand seems to be particularly responsible for this “substrate effect” in the utilization of iron‐III‐hydroxide. The uptake of phosphorus and iron in sequence along a root growing in a solid substrate could be important in the iron nutrition of “iron‐inefficient” plant species such as corn growing in soils of high pH.