A comparison of indigenous soil factors influencing the Fe‐deficiency chlorosis of sorghum and soybean in calcareous soils

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Abstract
The factors influencing Fe‐deficiency chlorosis in plants may be subdivided into the following general categories: indigenous soil, environmental, nutritional and microbial. Indigenous soil factors include those soil properties over which we have little or no control such as clay mineralogy, CaCO3 reactivity, Fe‐oxide content and reactivity, organic matter content, and exchange ion composition. The objective of this paper is to compare results of previous studies of sorghum (Loeppert and Hallmark, 1985) and soybean (Morris et al., 1987) with regard to the indigenous soil properties that play the dominant roles in influencing Fe chlorosis. Fe‐inefficient cultivars of sorghum and soybean were each grown in sand/soil mixtures of 24 calcareous soils which were selected to obtain ranges of CaCO3, Fe oxide, clay and organic matter contents. The soil Fe oxide played a dominant role in influencing the availability of Fe, with both sorghum and soybean, and the amorphous Fe‐oxide content was negatively correlated with the incidence of Fe chlorosis. Reactivity of the carbonate phase, total carbonate surface area and quantity of clay‐size carbonate were each positively correlated with the incidence of chlorosis of soybean, but there was no evidence of a similar influence with sorghum. Soil solution Mg concentration was positively correlated with incidence of chlorosis in both sorghum and soybean. These results are discussed in terms of theoretical Fe‐deficiency stress‐response models.