Some modifications in trace metal toxicities and deficiencies in plants resulting from interactions with other elements and chelating agents‐‐the special case of iron

Abstract

Whenever land becomes contaminated with trace metals, most always two or more of the trace metals are in excess simultaneously. Nearly all of the baseline studies of metal excesses, however, have been made with single metals, and such studies do not accurately reflect the critical response levels. Various critical points can shift due to interactions. Analytical data must be obtained for as many as 20 different elements and their differential distribution among various plant parts, including roots, must be known to gain even a partial understanding of the interactions. Positive and negative synergisms, competition, protection, and sequential additivity are observed among the interactions. The nature of interactions varies considerably with concentration levels, soil pH, soil texture, level of soluble Ca in soil, presence of salinity, differential distribution in soil of the metals present in toxic quantities, presence or absence of chelating agents, soil organic matter levels, and other factors. Interactions are difficult to model. All of these relate to the behavior of Fe in plants and in soil. Iron deficiency is commonly induced by excess levels of other trace metals, both singly and more commonly in various combinations. Such Fe deficiency is complex. Other essential nutrients are involved in somewhat similar interactions. When testing soil for possible problems with Fe deficiency, it is important that concentrations of available trace elements other than Fe in addition to other soil parameters be considered in the equation for prediction.