Micronutrient deficiencies represent an ongoing limitation to agricultural productivity in Southern Australia and in many regions of the world. Micronutrient deficiencies are commonly encountered on alkaline and calcareous soils due to their high metal adsorption and fixation capacities. Chelating agents, such as EDTA, are used to reduce fertilizer fixation in these soils. However, EDTA can be relatively ineffective on alkaline soils and may have negative environmental implications due to its long-term persistence.

We have examined two novel chelating agents for use on alkaline and calcareous soils.  The novel chelates differ significantly from EDTA in terms of their structure and functionality. For example, Rhamnolipid is produced by Pseudomonas bacteria, is non-toxic, biodegradable and forms a lipophilic complex with cationic metal ions. We have also examined polymeric chelating agents that can complex up to 4 times more metal (g Cu(II)/g ligand) than EDTA, which has important implications for the cost effectiveness of chelate use.

Solution culture experiments have shown that the novel chelating agents increase the kinetic rate of Zn absorption into the root symplast, compared with ZnCl₂ alone. On alkaline and calcareous soils the novel chelates were significantly (P<0.05) more effective Zn sources than EDTA or the SO₄^2- salt. EDTA increased the concentration of Zn in soil solution. However, this did not translate to increased Zn uptake by Canola plants. This was not surprising as EDTA inhibited Zn absorption by roots in the solution culture experiments.

Our results showed that, on alkaline soils, chelates that increased the rate of micronutrient absorption into the root symplast were significantly more effective than EDTA, which was not readily absorbed by canola roots. These results have important implications for future fertilizer development, the cost effectiveness of chelate use and the treatment of micronutrient deficiencies on alkaline soils in the world today.