| Summary: | <p>Phosphogypsum (PG) is a by-product of the P fertilizer industry usually valorised as amendment for acidic and sodic soils. This work was aimed to study the effects of PG on nutrient uptake by industrial tomato plants in an originally sodic soil. A completely randomized experiment was performed involving two factors: (i) acidification with nitric acid (mimics cleaning techniques in drip irrigation), and (ii) PG rate (equivalents to 0, 20, 60, and 200 Mg ha<sup>–1</sup>). The highest PG rate resulted in an increased dry matter yield, which can be ascribed at least in part to an increased water use efficiency. PG decreased K, Mg and P concentrations in shoots, and P and Cu concentrations in fruits. At the highest rate, PG increased B concentration in shoots and total B content in the aerial parts of plants when acid was applied. The highest PG rate also increased Ca concentration in fruits, which can be considered positive in view of reducing the incidence of blossom end rot. The total content of Ni and Mo in aerial parts increased with PG, probably related to a decreased adsorption of these nutrients in soils. Acid application increased the concentration of all micronutrients in shoots and the concentration of Fe, Cu and B in fruits. In conclusion, PG promoted positive effects on B, Ni, Mo, and Ca nutrition, and some negative nutritional effects through antagonisms or affecting nutrient cycling in the soils, which however did not result in decreasing yields, even at a large dose which mimics the cumulative application during 20-30 years. Acid treatments resulted in improved micronutrient nutrition of tomato plants.</p>
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