WATER AND MINERAL DEMAND OF GREENHOUSE SOILLESS ROSE CROPS GROWN UNDER SUMMER CONDITIONS

Water demand and mineral absorption of soilless rose plants were studied in a 100 m2 glasshouse situated in Antibes, from summer 92 to spring 93, with 3 different nutrition levels (3.5, 7 and 14 mMol/l NO₃). Mean values over a few days are obtained from mineral balance in a still medium (static feeding). Hourly variations are obtained by analysing the mass and composition of a rapidly recycling limited volume of fresh solution (dynamic feeding).

Transpiration rates observed under moderate insolation appear to be quite similar in all treatments and to closely follow the solar radiation pattern, for static or dynamic feeding as well.
But under strong irradiation and for static feeding, the transpiration rate significantly depends on the nutrition level.

In both feeding regimes, the weaker solution is depleted in NO₃ by the plant, but does not exhibit any visible conductivity drop, while richer nutritions generate both Ec and NO₃ positive drifts in the medium, with a risk of salinity stress.

The composition of the absorbed solution sharply oscillates over a 24 hour period, from a low 3 mMol/l NO₃ around noon, to more than 25 mMol/l at night.

In static feeding, high concentration gradients may take place around the roots as the result of plant uptakes.
Switching to dynamic feeding cancels salinity gradients in the medium and can create a sudden negative concentration gap between roots and medium, evidenced here by NO₃ efflux.
It is thus suggested that dynamic feeding, able to wipe out such concentration gradients, could be used as a technique to lower salinity levels in the roots and reduce the partial stomatal closure observed under strong radiation with static feeding.

International Symposium on New Cultivation Systems in Greenhouse

A. Jaffrin, A. Champeroux, N. Pertusier

https://doi.org/10.17660/ActaHortic.1994.361.24