The effectiveness of soil-applied FeEDDHA treatments in preventing iron chlorosis in soybean as a function of the o,o-FeEDDHA content

The application of FeEDDHA products is the most common practice to prevent or to remedy Fe chlorosis in crops grown on calcareous soils. These products consist of a mixture of EDDHA components chelated to Fe. In this study such mixtures have been divided into four (groups of) components: racemic o,o-EDDHA, meso o,o-EDDHA, o,p-EDDHA and rest-EDDHA. Because the physical and chemical properties of these components differ, so does their effectiveness in delivering Fe to the plant. This effectiveness has not yet been examined in soil application, but needs to be understood to come to an adequate Fe fertilization recommendation. In this study the influence of composition of FeEDDHA treatments on Fe uptake by soybean plants (Glycine Max (L.) Merr. cv. Mycogen 5072) grown on calcareous soils was examined in two pot trials involving eight soils. The FeEDDHA treatments were equal in Fe dose but differed in o,o-FeEDDHA content, and were applied prior to the set in of chlorosis. The o,o-FeEDDHA content largely determined the Fe concentration in the pore water. In turn, in soils that induced chlorosis, the Fe concentration in the pore water determined the Fe uptake. The relationship between Fe concentration and Fe uptake is non-linear: initially Fe uptake increases strongly with increasing Fe concentration, but the slope flattens and a plateau is reached. FeEDDHA treatments increased both yield (up to 30%) and Fe content of the plant tissue (up to 50%). From FeEDDHA products with a higher o,o-FeEDDHA content, a smaller Fe dose is required to obtain the same results in terms of yield and Fe nutritional value.