Sustainable crop fertilization by combining biogenic nano-hydroxyapatite and P solubilizing bacteria: Observations on barley

Nano-enabled agriculture involves researching smart nano-agrochemicals for sustainable farming. Nano-hydroxyapatite (nHAP), a phosphorus-rich compound, has the potential to be used as a fertilizer with reduced environmental impact. This study tests the effectiveness of nHAP produced from waste materials (animal bones) on barley plants (Hordeum vulgare). Two different nHAPs were prepared by thermal treatment of chicken bones at 300 °C and 700 °C (nHAP300 and nHAP700, respectively). The nanopowders were then tested in a seed toxicity trial and in a greenhouse pot experiment with barley, using Pseudomonas alloputida, a P-solubilizing bacterium (PSB). The treatments were unfertilized soil, conventional triple superphosphate (TSP), and the nHAP treatments alone. The results indicated that: (i) the nHAP materials had particle sizes of 1 micrometer (nHAP300, due to aggregation) and 50–70 nm (nHAP700), with P contents of 12.8 % and 19.6 %, respectively; (ii) no toxicity was observed on barley seeds, and nHAP300 at maximum dose stimulated root length by 45.6 % compared to the control; (iii) compared to conventional P fertilizer TSP, nHAP300 and nHAP700 stimulated root growth by 7 % and 18 %, respectively; (iv) the fraction of available P produced through nHAP300-PSB (40.6 mg kg−1) was higher than that from TSP (39.2 mg kg−1); (v) ions associated with the nHAP structure supplied supplementary nutrients, predominantly allocated in root tissues. This study provides valuable insights for future investigations to assess the implications of P nano-fertilizations in achieving sustainability in agriculture.