Irrigation management requires a combination of several tools, but it may not be necessary to apply/use all of them. Irrigation management tools should be chosen by the winegrower according to the various constraints involved (cost, time).
o Soil analysis: It is useful to dig soil pits at the base of the vines to learn about their root system (depth, volume, types of roots). This information can help explain how the vine functions and its potential water needs. Tensiometry measurements with a probe can be used in addition to other observations when managing irrigation. They enable the soil's capacity to retain water to be determined. The measurement scale is between 0 and 200, the higher the value, the less water is available, and the more the water provided will need to be spaced out and in smaller quantities.
o Weather: The installation of one or more weather stations in the vineyard helps to provide weather information on a continuous basis and according to the plot's microclimate. There are also water stress bulletins published during the grape ripening period, which include all the field data recorded. This data also makes it possible to estimate the vines' evapotranspiration and provides additional information for irrigation management.
o Vineyard observation: Visually inspecting the vineyard is often the first method for identifying water shortages. Observation of leaf colour provides useful information: yellowed leaves can indicate a significant lack of water (but can also mean there is a magnesium deficiency). Close observation of the apex morphology (the growing tips of the shoots) is also essential to easily follow the water regime of the vines. This is achieved by folding the last two unfolded leaves upwards along the apex. When 50% of the leaves are growing faster than the branches (i.e. cover the apexes), the growth of the apexes has slowed, which indicates that water stress is low to moderate. When 50% of the leaves exceed the apex and/or when the apexes are dry or necrotic, the water stress is severe.
o Additional measurements and monitoring: Other measurements that vary in terms of cost and time required can be set up in the vineyard throughout the growth cycle in order to obtain information on the vines' water regime and enable better irrigation management. Leaf water potential (expressed in MPa) for example is measured with a pressure chamber before daybreak, when the plant has rebalanced its water status with the water reserves available in the soil. Stem water potential is measured in the middle of the day, when the vine is under the most stress. Other tools are also used to characterize the vines' water regime, such as the 13C/12C isotope ratio or the leaf temperature measurements. NDVI (Normalized Difference Vegetation Index) maps can be taken at different times in the growth cycle for the entire vineyard. It is a useful tool for visualizing the water status of the vineyard as a whole during and/or across vintages.