FAQ

Frequently Asked Questions

• How can sap flow sensors be useful to improve vineyard management?

  Sap flow measures plant transpiration every 15 minutes. Plant transpiration variations can be analyzed throughout the season to better understand how it affects fruit composition and to better characterize plant water status.

• How can irrigation be optimized using sap flow in real time?

  Everytime an irrigation is performed we observe an increase in plant transpiration. As a result sap flow gets higher. The effect of an irrigation can be characterized by looking at how high and during how many days transpiration peaks after a water addition. If the goal of irrigation is to avoid dehydration symptoms, sap flow monitoring ensures that sufficient plant transpiration happens between irrigations. Sap flow monitoring also ensures that plant transpiration does not fall below critical levels when important plant water deficit is beneficial for the fruit quality (like before fruit veraison stage).

• How does it compare to soil moisture sensors?

  Soil moisture sensors can give a good estimate of soil moisture content after irrigation. However, only a fraction of the root system can "see" the local increase in soil moisture content measured by soil moisture sensors. For that reason, particularly when root system is deep, it is difficult to quantify how much soil water is available to the root from simply reading soil moisture content. As a result soil moisture sensor reading can correlate very poorly with plant transpiration and is not often a reliable tool to make irrigation decisions.

• How does it compare to pressure bomb readings?

  Pressure bomb reading gives an information relative to the "tension" of the water circulating between the plant and the air. When the water tension gets higher, we read more negative values. Indirectly, this also indicates that less and less water is going through between the plant and the air. Sap flow gives an information relative to the "amount" of water circulating between the plant and the air. When the sap flow gets lower, it means directly that less and less water is going through between the plant and the air. To make an analogy with every day life, water molecules flowing through the plant can be compared with electrons flowing through an electrical wire. In one hand, measuring water tension with a pressure bomb becomes like measuring an electrical tension between 2 points with a Voltmeter when one wants to know the electrical current between those 2 points. In the other hand, measuring water flow between the plant and the air becomes like directly measuring an electrical intensity between 2 points.

• What is the effect of soil composition on sap flow?

  Sap flow directly reflects the effect of soil composition on plant transpiration. When water is tightly bound to soil particles, root water uptake is lower and therefore sap flow is lower. Monitoring sap flow variations can also be considered as a way to characterize how soil composition directly affects plant transpiration.

• How does sap flow vary?

  Plant transpiration is the result of the interaction existing between weather demand and soil moisture available to the roots. Throughout the season, the plant integrates "signals" coming from the roots and from the weather demand to constantly regulate its own transpiration.