Impact of mineral and organic fertilisation practices on elemental authenticity signature on apple Royal Gala from protected geographical indication (PGI) “Maçã de Alcobaça”

Abstract

Market demand, climate change and soil degradation force producers to maintain the productivity and quality of high-market-value products, such as Protected Geographical Indication (PGI) fruits. “Maçã de Alcobaça” apples produced in the central-western part of Portugal, namely the variety Royal Gala, one of the PGI varieties with higher demand, are among those with higher requirements in terms of fertilization to maintain the high productivity demanded by the market. In the present work, three different soil NPK fertilization schemes were applied to experimental orchards within the PGI area (1 x mineral NPK proposed for integrated production, an intermediate strategy that included organic granular amendment and 2 x mineral NPK), and the elemental profiles of the apple pulps were analysed and compared. Some mineral elements improved their concentration in the apple pulps with fertilization due to interactions of these elements with the fertilizer components (namely, nitrogen, potassium and phosphorus) or to potential changes in the bioavailability of the elements in the soil due to fertilization application. From a nutritional perspective, enhancing the mineral profile of apple pulps can be achieved by applying 1 x NPK fertilization. Consuming an average of 2 fruits daily (160 g each) would then help meet a higher percentage of the daily requirements for most essential elements crucial for human nutrition. Also, noteworthy to mention, that none of the tested fertilization practices led to a reduction in the nutritional quality of the fruits analysed when compared to the 1 x NPK condition. The present work also had the objective of evaluating if these fertilization practices and the mineral changes induced would have implications for the PGI authenticity elemental signatures previously developed. Using Partial Least Squares-Discriminant Analysis (PLS-DA) models calibrated with PGI and non-PGI (from North Portugal and Italy) samples and feeding these models with elemental profile data of fruits collected from fertilized orchards as blind samples, it was possible to observe that all samples from the fertilization trials were correctly classified as PGI samples. This reinforces the edaphic characteristics of the cultivation area's prevalent role over the effect of fertilization practices or physiological trait changes, in shaping the elemental signature of the fruits. This was found to be mostly due to the high influence of geologically linked elements (such as Rb, Pb and Y) in the discrimination of the sample provenance. This allows us to confirm the suitability of the elemental traceability models for “Maçã de Alcobaça” PGI authenticity validation, ensuring its provenance and nutritional characteristics to the consumers and maintaining its market value even if fertilization practices are applied to fight less favourable cultivation conditions.