The aim of this research is to develop an analytical methodology for the determination of complexed element in fertilizers and, then, to obtain an adequate criteria for the inclusion of these products in European Regulations on Fertilizers. This paper compares the CEN method EN 13366:2001, based on the retention of the cations into a sulfonated resin, and an AOAC modified method, based on the precipitation of the inorganic forms at pH 9. A limited interlaboratory trial was carried out to demonstrate the applicability of the AOAC modified method and to study the effect of the removal of organic compounds and the addition of a matrix modifier solution before the element quantification. Then, a global interlaboratory trial was developed to evaluate the validation and quality parameters of the method. As a second objective, the AOAC modified method was applied to the determination of the complexing capacity of complexing agents based on lignosulfonates and amino acids. The AOAC modified method was the choice methodology because it is adequate for the determination of complexing capacity of micronutrients in fertilizer.

In the past several years, concern about the environmental fate of recalcitrant synthetic ligands (e.g., EDTA) has increased. The used of new biodegradable chelating agents such as imidodisuccinic acid (IDHA) has been proposed as an alternative. However, its application as an iron ligand to correct iron chlorosis in agriculture has not yet been studied. Then the objective of this work is to determine the fertilizer capacity of IDHA/Fe3+ using interaction assays with soils and soil materials and evaluating Fe nutrition of efficient and susceptible plants. Interaction of IDHA/Fe3+ with soil materials produces a reduction of the amount of soluble Fe. This is in good agreement with studies on the stability of the IDHA/Fe3+ chelate. In general, plant response to IDHA/Fe3+ in hydroponics is acceptable and better than that to EDTA/Fe3+. This good behavior seems to be related to the lower coordination of the iron in IDHA/Fe3+ with respect to EDTA/Fe3+.

A gronomy J our n al • Volume 10 0 , I s sue 3 • 2 0 0 8 813 ABSTRACT Th e new biodegradable chelating agent imidodisuccinic acid (IDHA) has been studied for its application in agriculture. Th is study was conducted to compare the effi ciency of mixed IDHA and ethylene diamine tetraacetic acid (EDTA) formulations to provide Fe, Mn, Zn, and Cu to green bean (Phaseolus vulgaris 'Perfección negra polo') and tomato (Lycopersicum esculentum Mill. 'Shiren') plants grown in greenhouses in soil-less and soil cultures in fertigation conditions. Th e eff ect on micronutrient concentrations, SPAD index and fruit yield were investigated. In the green bean experiment, control (no chelate applied) plants showed important micronutrient defi ciency symptoms and growth reduction, while IDHA treated plants were healthy. Although EDTA provides micronutrients in higher amounts than IDHA, a chryptogamic infection was observed for this treatment but not for the IDHA one. In the tomato grown on rockwool experiment, increments of SPAD index and Zn concentration are higher in plants treated with IDHA than with EDTA, though for the tomato on soil mulch experiment no diff erences were found among treatments, even the control. Th e results are in agreement with previously published studies on the behavior of IDHA. Th e new chelating agent IDHA can substitute EDTA in hydroponics and fertigation cultures as a chelating agent for micronutrients.

Naturally derived complexes with the ability to complex (unidentate) or chelate (polydentate) metals are a cheaper alternative to synthetic chelates to correct micronutrient deficiencies, but despite their widespread use there is a lack of knowledge on their agronomic performance. The aim of this paper was to evaluate the stability of iron (Fe) and zinc (Zn) lignosulfonate, gluconate, amino acid, and humate complexes in solution over time and at different pH values. Also, their stability in a concentrated nutrient solution and their reactivity with soils and soil components was evaluated. In our experimental conditions, all the complexes (except Fe amino acid) remained stable in solution for an extended period of time. All Zn complexes and the Fe lignosulfonate were stable in solution up to pH 7.0–7.5, while Fe gluconate only maintained 20%–40% of the iron in solution in the pH range 5–11 and Fe amino acid and humate complexes barely maintained small concentrations of Fe in solution above pH 3. Most of the complexes maintained Fe and Zn in concentrated nutrient solutions for irrigation systems, but Fe amino acid only maintained around 70% of the iron added. In general, the interactions of complexes with soils and soil components produced a high retention. The interaction of Fe lignosulfonate with peat, illite, and ferrihydrite, and Fe gluconate with peat and illite resulted in significant amounts of Fe to remain in solution, while for the Fe amino acid and humate the Fe remaining in solution was low. All Zn complexes were highly retained in an acidic peat, illite, and montmorillonite clays and soils, while no retention was observed on ferrihydrite. In conclusion, the stability of complexes in different conditions is related to the percentage of complexed element in the products. While complexes can be used to maintain micronutrients in solution in aqueous media (foliar and fertigation), their application to soil should be considered as a measure to increase metal availabilities but not their solubility.