Use of the stable isotope (57) Fe to track the efficacy of the foliar application of lignosulfonate/Fe(3+) complexes to correct Fe deficiencies in cucumber plants.

BACKGROUND: During the last decade, environmental concerns regarding the use of recalcitrant synthetic chelates to overcome iron chlorosis has increased and new ligands such as lignosulfonates (LS) have been evaluated. However, the efficacy of these products is variable. In this work a hardwood (eucalyptus) and softwood (spruce) LS were compared to try to relate their physico-chemical characteristics and their efficacy. Also two more products derived from the eucalyptus lignosulfonate were tested. RESULTS: All the LS tested presented a good ability to complex Fe, but only the spruce LS was capable to maintain significant amounts of soluble Fe above pH 8. According to the FTIR data, structural changes related to the Fe source (Fe(2+) or Fe(3+) ) used to form the complex occurred in the LS molecule and might influence their efficacy. Cucumber (Cucumis sativus L. cv Ashley) chlorotic plants were used to test lignosulfonate efficacy when applied through foliar sprays in comparison with FeSO(4) and EDTA/(57) Fe(3+) . The (57) Fe content of plants sprayed with LS was very low in respect to the EDTA treatment, but this was not reflected in the biomass and re-greening rates. Eucalyptus LS modifications improve its efficacy for iron chlorosis recovery to levels similar to those found for the spruce LS. Two applications of the LS are recommended. CONCLUSIONS: Lignosulfonates did not require surfactants for their application; they did not burn the leaves, and had a stimulating effect on the vegetative growth of the plants. So these by-products could be a good alternative when applied through foliar sprays for cucumber plants.

Iron supply to soybean plants through the foliar application of IDHA/Fe3+: effect of plant nutritional status and adjuvants.

BACKGROUND: Synthetic Fe chelates are commonly used to overcome Fe deficiencies in crops, but most of them are scarcely biodegradable. Iminodisuccinic acid (IDHA) is a biodegradable chelating agent that is currently being evaluated as an alternative to EDTA. In this work, the efficacy of the foliar application of IDHA/Fe(3+) to soybean chlorotic plants under controlled conditions was studied, testing the influence of the adjuvant used and of the plant nutritional status. RESULTS: When IDHA/Fe(3+) was applied to soybean plants with severe Fe chlorosis and the foliar sprays were the sole source of Fe, this chelate behaved similarly to the EDTA/Fe(3+) and the recovery of the plants was slight in both cases. The same chelates were tested when foliar sprays were an additional source of Fe for mildly chlorotic plants, which were also being supplied with low concentrations of Fe applied to the nutrient solution. Then, plant recovery was appreciable in all cases, and the IDHA/Fe(3+) was as effective as EDTA/Fe(3+). Among the adjuvants studied, a urea-based product was the only one that did not damage the leaf surface and that could improve the efficiency of IDHA/Fe(3+) up tp the level of EDTA/Fe(3+). CONCLUSIONS: Thus, it was concluded the foliar application of IDHA/Fe(3+) can be an environmentally friendly alternative to the non-biodegradable chelate EDTA/Fe(3+) when the appropriate adjuvant is used.

Revalorization of a two-phase olive mill waste extract into a micronutrient fertilizer.

Micronutrient deficiencies in plants may be treated using metal complexes. A modified two-phase olive mill waste (OMWm) was characterized using FTIR spectroscopy. A study was also made of micronutrient (Fe, Zn, Mn and Cu) complexation and the stability of complexes. An evaluation was then made of the effectiveness of Fe(III)OMWm to supply Fe to soybean (Glycine max. cv Stine 0480) chlorotic plants through nutrient solution and foliar application. The OMWm presented structural similarities with the fulvic fraction of raw OMW containing abundant phenolic-hydroxyl and carboxyl groups able to form complexes. The OMWm could complex Fe, Zn, Mn and Cu, although the stabilities of the complexes under agronomic conditions were low. In dealing with Fe chlorosis, Fe(III)-OMWm improved the Fe nutritional status of soybean chlorotic plants when applied to the nutrient solution, while only regreening of leaves was observed in foliar applications. Hence, OMWm complexes constitute a promising eco-compatible and cheap alternative to synthetic chelates in dealing with micronutrient deficiencies when applied foliarly or to the nutrient solution, although further research is necessary to improve the stability and effectiveness of the complexes.