ACTA HORTICULTURAE

A study has been undertaken in order to look for relationships between the crop mineral uptake (rose plant 'Dallas') and the climatic variables that influence the transpiration and assimilation processes. A 30 plants unit grown in a NFT system under a polyearbonate greenhouse has been used. High positive correlations were obtained between the nitrate uptake rate, NUR, and the water uptake rate, WUR, and between the nitrate uptake rate and the nutrient solution temperature during the summer under an aluminized shading screen which covered the polyearbonate. WUR and the integral of the solar radiation of the previous hours are the regression variables during the diurnal time. High positive correlations were found in the winter between the NUR and the cumulated solar radiation, and a lower correlation was obtained between the NUR and the solution temperature. In the winter, the correlation with solar radiation was lower for the 24 hr. cycle. Highest radiation hours had a correlation with the radiation integral of the 4 previous hours. The daytime NUR maxima were measured in the summer with values as high as 0.145 mmol de NO3-.h(-1).pl(-1), as compared to the 0.08 mmol de NO3-.h(-1).Pl(-1) measured in the winter. During the night, small differences were obtained between the summer and winter maximum NUR, around 0.05 mmol de NO3-.h(-1).pl(-1). Night to total day NUR ratio was small. The largest differences in nitrate uptake concentration, NUC, along the 24 hr period, were obtained during the night time (from 22 to 05 solar time), with higher values for the summer than for the winter. In the central hours of the day (from 10 to 17 solar time) summer to winter differences are not so obvious (2.173 and 2.099 mmol NO3-.l(-1).h(-1), respectively). The winter NUC values are quite stable, with minimal variations all along the 24 hour cycle.