Can the Application of Microbial Inocula Allow for Reducing Phosphate Fertilisation Rates in Open Field Tomato Crops?

In addition to its obvious benefits, mineral fertilisation also poses a number of threats to the environment. A four-year study was conducted to verify the possibility of integrating the application of a bacterial consortium to reduce the dose of mineral phosphorus (P) fertilisers in field-grown tomato crops without negative effects on yield. The combination of the microbial consortium with a 60% dose of both simple and complex P fertilisers did not show statistical differences in crop productivity and fruit quality compared to the full dose fertilisation each year, even when considering the cumulative yield. This was paralleled by a similar level of leaf chlorophyll index. Plants grown in rhizoboxes showed that the inoculation favoured, in the case of the complex fertiliser, a modification of the root system architecture, though not confirmed statistically. In the case of this kind of fertiliser, the inoculation induced a significant increase in the rhizospheric bacterial metabolic activity, which could be partly accounted for by the agronomic performance. However, this was not paralleled by a modification of the metabolic biodiversity of the bacterial population. The study demonstrated that, for highly demanding crops such as tomato, a valid agrononomic target for the application of microbial-based products integrated into a reduced mineral P fertilisation strategy could reach crop productivity not different from that obtained without them. Such a strategy could favour the adoption of an integrated nutrient management strategy by farmers, with positive impacts also on the environment.