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Growth, N uptake and light interception were studied in processing tomato grown in the field in Central Italy (Tiber Valley, 43°N, elev. 165 m) at different levels of fertiliser-N in 1996–97–99. Plant N concentration declined during the entire crop cycle. The relationship between the total above-ground dry biomass (DW, Mg ha−1) and critical N concentration (%Nc, the minimum N concentration required for maximum plant growth, calculated according to Justes et al., Ann. Bot., 1994, 74, 397–407) was %Nc=4.53 DW−0.327 for total-N, and %Nc=3.90 DW−0.270 for reduced-N. The critical dilution curves were applied when the above-ground dry biomass varied between 1.2 and 12.4 Mg ha−1 and for stages of development ranging from the onset of fruit growth (∼40 days after transplanting) to maturity. Increasing N availability increased dry matter accumulation. Relationships between crop total-N uptake (Nupt, kg N ha−1) and accumulated dry matter in the aerial biomass (DW, Mg ha−1) fit very well to the model Nupt=10 a DW 1−b (Lemaire and Salette, Agronomie, 1984, 7, 381–389) for each fertiliser-N level in all three experiments. In all years the ‘critical uptake’ curve (Nupt=45.3 DW 0.673) was between the uptake curves obtained with the fertiliser-N rates of 100 and 200 kg ha−1. Increasing N supply increased the amount of absorbed PAR accumulated throughout the growth cycle and slightly affected the Radiation Use Efficiency. Results are discussed also taking into account the effect of N availability on source-sink relationships. [Copyright &y& Elsevier]

Abstract Selenium (Se) is a trace element necessary for both human and livestock nutrition. To increase Se human intake, soil Se fertilizations were performed but the fate of the added Se remains unclear. The present research aims to: (1) determine the influence of Se fertilization on the fractionation of Se in soil; (2) assess the influence of water availability on the distribution of soil Se chemical fractions; and (3) monitor the Se content in soil, leachates and plants. To reach these goals, 200 g Se ha−1 was applied to soil as sodium selenite in maize crops under two irrigation regimes, and the Se content in plant, soil chemical fractions and leachates were analyzed. Se application increased the total Se content of the soil, specifically it increased the Se content of the soluble, exchangeable and organic fractions with more pronounced effect in the soils with higher water availability. These differences disappeared over time likely due to the Se loss through volatilization. The hypothesis of Se volatilization is confirmed by the absence of both leachates during the maize growing season and differences among the treatments of Se content in sub-soil samples. Also, although the Se treated plants showed higher Se content than the untreated ones, overall <1% of the added Se was assimilated by plants. Hence, this study demonstrated that the addition of selenite to the soil increased the Se contents of the plants, but the Se does not accumulate in the soil because it is likely lost via volatilization. Further, leaching of Se into groundwater is avoided due to its association with both the soil organic matter and positively charged binding sites of soil, and due to its loss via volatilization. Therefore, soil Se fertilization could increase the nutritional value of plants without consequences on the environment. Graphical abstract Unlabelled Image Highlights • The fate of selenium fertilizer was investigated in soil during maize cropping. • Soil selenium chemical fractionation was performed. • The Se content in soil fractions, leachates and plant tissues was evaluated. • Se fertilization increases the soil Se availability and the Se content in plant. • Soil Se is lost overtime through volatilization and not by leaching. [ABSTRACT FROM AUTHOR]