GRENNHOUSE TOMATO CROP TRANSPIRATION MODEL APPLICATION TO IRRIGATION CONTROL.

Greenhouse climate and transpiration of a soilless tomato crop was recorded and analyzed together with a complete transpiration model during a whole croping period from March to August.

A simple model of transpiration (TR) based on the combination method (Penman-Monteith formula) was derived:

This model sub-divide the transpiration in two components : a radiative part (proportional to the radiation absorbed by the crop RG_abs) and an advective part (proportional to the greenhouse air water vapour pressure deficit : D_a)

The partition of the transpiration between these two components was measured and it was shown that the advective term including the air vapour pressure deficit cannot be neglected in greenhouse conditions.

In order to improve short term prediction of irrigation, A and B were calculated:

• either directly, through the appliance of the complete model of transpiration ;
• or by a statistical identification, knowing the transpiration and the climatic parameters.

Both methods show a good agreement for A and B determination and evidence a variation of their values between diurnal (maximal) and nocturnal (minimal) period. Algorithms improving on-line irrigation prediction as a fonction of the global radiation and vapour pressure deficit were derived. They were incorporated in a commercial fertirrigation computer software. At present this program is tested in comparaison with a classical irrigation method.