FePO nanoparticles produced by an industrially scalable continuous-flow method are an available form of P and Fe for cucumber and maize plants.

Nanomaterials are widely used in medical and pharmaceutical fields, but their application in plant nutrition is at its infancy. Phosphorous (P) and iron (Fe) are essential mineral nutrients limiting in a wide range of conditions the yield of crops. Phosphate and Fe fertilizers to-date on the market display low efficiency (P fertilizers) and low persistence in soil (Fe fertilizers) and negatively affect the environment. In the tentative to overcome these problems, we developed a continuous industrially scalable method to produce FePO NPs based on the rapid mixing of salt solutions in a mixing chamber. The process, that included the addition of citrate as capping agent allowed to obtain a stable suspension of NPs over the time. The NPs were tested for their effectiveness as P and Fe sources on two hydroponically grown crop species (cucumber and maize) comparing their effects to those exerted by non-nanometric FePO (bulk FePO). The results showed that FePO NPs improved the availability of P and Fe, if compared to the non-nano counterpart, as demonstrated by leaf SPAD indexes, fresh biomasses and P and Fe contents in tissues. The results open a new avenue in the application of nanosized material in the field of plant nutrition and fertilization.