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Iron Uptake by Two Citrus Rootstock Species in Relation to Soil Moisture and CaC0₃¹

Pot cultures were used to study the effects of soil water suction, presence of CaCO₃ in the soil, and two species of rootstock, Citrus Aurantium L. and Citrus sinensis (Linn.) Osbeck, on iron uptake and iron sufficiency. Iron concentration in standard leaf samples was used as the measure of iron sufficiency; total leaf iron per plant was used as the measure of uptake.

Iron uptake was proportional to the weight of the root system (r = .92) when water suction was varied; this supports the hypothesis that iron uptake from aerated soils depends primarily on contacts between root surfaces and iron-bearing soil particles.

Differences in iron uptake not accounted for by root size are described in terms of "root efficiency", expressed as µg of leaf iron per gram of roots. Addition of CaCO₃ to the soil markedly reduced the efficiency of sweet orange roots but affected that of sour orange roots only slightly, which suggests that the transfer of iron from soil to root involves two or more mechanisms that are differentially sensitive to CaCO₃.

Sufficiency of iron supply to the plants was correlated with root: top ratio (r = .73 when water suction was varied; r = .72 when both soil CaCO₃ and rootstocks were varied), lit is concluded that physical dimensions of the iron source (roots) and sink (tops) are important plant factors that regulate iron sufficiency in the plant.

Key Words: iron sufficiency • soil water suction • root:top ratio • root efficiency

² Associate Professor of Soil Science, Department of Soils and Plant Nutrition; Professor of Biometry, Biometrical Laboratory.

Received for publication June 1, 1967.