Response of a plurispecific permanent grassland to border irrigation regulated by tensiometers
Réponse d'une prairie permanente pluri-espèces à une irrigation gravitaire par calans pilotée par tensiométrie
Résumé
To improve Water Use Efficiency (WUE) of border irrigation, we investigated an integrated approach of Tensiometric Regulated Irrigation considering both crop response (yield and quality) and water dynamic. In the Crau region, we studied plurispecific and permanent grasslands with high quality hay production which are irrigated by border irrigation. Soil Water Potential (psi total) was used to schedule irrigation and diagnose mild water deficits. Neutron probe measurements were used to quantify the soil water deficit experienced by the plant with the Fraction of Transpirable Soil Water (FTSW). The dynamic of aboveground dry matter production and botanic composition were analysed in reference to FTSW. The results show the extreme sensitivity of grasslands to mild Soil Water Deficit experienced by plants between two dates of irrigations. Across the range of soil water deficit observed in these experiments both hay production and botanical composition were closely related to the average FTSW. Aboveground biomass was rapidly stopped when FTSW reachs 60% and botanical composition was also significantly changed by these water deficits. The agreement between soil water measurements and grasslands response indicates that Regulated Deficit Irrigation based on soil water potential or FTSW can be used to optimize border irrigation in these conditions where the trade-off between water saving and profit losses by mild water deficit is not easy to manage.