Bull. Spec. CORESTA Congress, Brighton, 1998, p. 97, A11

Irrigation scheduling of Virginia tobacco using Watermark sensors

BRACHET P.
ANITTA, Bergerac, France
A collaborative study on the use of water tension, as measured by Watermark sensors, to monitor irrigation was conducted in Western France in 1997 by three tobacco cooperatives, and coordinated by ANITTA. The objective of the experiment was to assess the effects of various levels of water supply on the growth and chemical composition of tobacco leaves. Methods: Three growing stages were considered: rooting, growing, maturity; in the experiment, each of these stages was investigated under two levels of water supply, one high, one low, those levels being defined in terms of water tensions in the soil. Irrigation was triggered by water tension levels, predefined in accordance with the type of soil. Each of the 8 treatments was grown on 6 rows of 100 m. Each variant includes three observation areas, each equipped with 4 sensors at various depths (2/3 of the plough zone, full depth of the plough zone, upper subsoil, lower subsoil: e.g. for a 30 cm depth of the plough zone, sensors were placed at depths of 20, 30, 40 and 60 cm), a rain gauge and a soil thermometer. Each variant was irrigated with micro-sprays placed every 2 metres alongside a central irrigation line. Preliminary conclusions:The tension retained for the high level of water supply corresponds to the time of consumption of the easily available reserve at the depth of 2/3 of the plough zone for the first two growing stages and full depth of the plough zone for the stage of maturity. No difference in development (precocity, maturity) was observed. Variants with thicker leaf tissue, dull colouring, low flexibility, are often those grown in conditions of short water supply during the growing phase and particularly at the end of the topping and sucker inhibition phase.Another full-scale experiment was conducted by another cooperative, with the objective of assessing the effects on tobacco yield and quality, but was unfortunately lost.Another series of trials will be conducted in 1998 to further investigate the trends observed in 1997.