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Micronutrients are essential factors for human health and integral for plant growth and development. Among the micronutrients, zinc (Zn) and iron (Fe) deficiency in dietary food are associated with malnutrition symptoms (hidden hunger), which can be overcome through biofortification. Different strategies, such as traditional and molecular plant breeding or application of chemical supplements along with fertilizers, have been employed to develop biofortified crop varieties with enhanced bioavailability of micronutrients. The use of microorganisms to help the crop plant in more efficient and effective uptake and translocation of Zn and Fe is a promising option that needs to be effectively integrated into agronomic or breeding approaches. However, this is less documented and forms the subject of our review. The major findings related to the mobilization of micronutrients by microorganisms highlighted the significance of (1) acidification of rhizospheric soil and (2) stimulation of secretion of phenolics. Plantmicrobe interaction studies illustrated novel inferences related to the (3) modifications in the root morphology and architecture, (4) reduction of phytic acid in food grains, and (5) upregulation of Zn/Fe transporters. For the biofortification of Zn and Fe, formulation(s) of such microbes (bacteria or fungi) can be explored as seed priming or soil dressing options. Using the modern tools of transcriptomics, metaproteomics, and genomics, the genes/proteins involved in their translocation within the plants of major crops can be identified and engineered for improving the efficacy of plant-microbe interactions. With micronutrient nutrition being of global concern, it is imperative that the synergies of scientists, policy makers, and educationists focus toward developing multipronged approaches that are environmentally sustainable, and integrating such microbial options into the mainframe of integrated farming practices in agriculture. This can lead to better quality and yields of produce, and innovative approaches in food processing can deliver cost-effective nutritious food for the undernourished populations.

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Three field experiments involving wheat, lucerne or cotton were established at different sites in the semiarid cropping regions of northern Australia, to test whether the deep placement of P fertiliser improved P availability, compared to the conventional practice of placing the fertiliser beside or adjacent to the seed. At Mulga View, near St George in southern Queensland on a red Kandosol soil with a Colwell soil test value of 19 mg P kg soil −1 in the top 10 cm, there was no response to 10 kg P ha −1 applied in the 5-7 cm layer. However, increasing the depth of placement of 10 kg P ha −1 from 5-7 to 10-15 cm resulted in increased shoot growth and grain yield of spring wheat (Triticum aestivum) by 43 and 30%, respectively. A further grain yield increase of 43% to 3.2 t ha −1 resulted when the deep P rate was increased from 10 to 40 kg P ha −1 . At Roma, in southern Queensland, on a grey/brown Vertosol with a Colwell soil test value of 15 mg P kg soil −1 , there was no difference in the winter growth of lucerne (Medicago sativa) when P fertiliser had been applied at 5-7 cm depth at rates of 10 and 40 kg P ha −1 . Shoot dry matter yields were around 2 t ha −1 . However dry matter yields increased significantly to 2.6 and 3.7 t ha −1 when 10 and 40 kg P ha −1 , respectively were applied at the 10-15 cm depth. The third experiment was carried out on a grey Vertosol at Kununurra in Western Australia. Significant increases in the yield of seed cotton (Gossypium hirsutum) occurred when 50 kg P ha −1 was applied at depth (10-15 and 25-30 cm), compared with the conventional placement at 7-10 cm, with maximum yield response to deep placement occurring with DAP, and the minimal response with MAP. The cotton was grown on raised beds and the crop was irrigated according to district practice. The response to deep P at all sites was attributed to the rapid drying of the soil surface layers, reducing the availability of soil or fertiliser P in these layers. The deep fertiliser P remained available during the growing season and alleviated the P deficiency that appears to be a feature of these soils when the surface layers become dry.