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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.

In the leaves of herbaceous plants sub-optimal temperatures influence the content and efficiency of the photosynthetic pigments and, in more severe cases, alter mesophyll thickness. This paper examines the possibility of detecting the degree of alteration in sorghum leaf characteristics by indices of stress calculated from remotely sensed data. Reflectance, colorimetric and ecophysiological measurements were performed on two cultivars of sorghum ( Sorghum bicolor (L.) Moench.) grown at 15, 21 and 32°C. Compared to plants grown at 21°C, the other two temperatures reduced chlorophyll content and PS II efficiency in the leaves, which were less at 15 than at 32°C. Slight differences in these responses to temperature were also observed between cultivars. Among the indices calculated, NDVI and RVI were able to detect not only the changes caused by the growth temperature but also the different responses of the two cultivars at the same temperature. Colorimetric coefficients detected a significant discolouration at 32°C and a marked reddening at 15°C. The indices calculated from the colorimetric data (CAI and D ( X i − X j )) were able to distinguish the differences between treatments, but they did not show a strict relationship with the trend of ecophysiological parameters.