Irrigation Management with the PHYTOGRAM™

Agricultural Electronics Corporation Home Page

PHYTOGRAM™ inside-the-plant hydration sensors provide users with an accurate and precise indication of a plant's need for water and the maximum amount that can be effectively utilized.

The internal hydration sensor consists of a thin noble metal rod. The sensor is implanted in the tissue of the plant. Hydration inside the plant wets the surface of this rod. The POD (chemical testing computer) senses changes in the area of this wetted surface. A very close analogy to this process is the use of an oil dipstick in the automobile engine. One senses the amount of oil in the engine by visually looking at the wetted area of oil on the dip stick. The PHYTOGRAM™ internal hydration measurement is a "water dipstick." The POD senses how much water is on the dipstick placed inside the plant.

The Diurnal Internal Hydration Cycle of the Plant

The diurnal cycle of the plant consists of two time periods: a water discharge period during the day and a water recharge period at night; in other words, water loss during the day and water replenishment at night. If the water recharge during the twenty-four period is equal to the water discharge, the internal hydration remains the same. If the water recharge is less that the water discharge the internal hydration decreases.

The complete diurnal cycles of water content will be placed on the Internet. There will be forty-eight data points per twenty-four hour period enabling appraisal of vine response to weather and irrigation at a half hour time resolution. At this time scale, it will be possible to determine the percolation rate, the part of the root profile that is responding to the irrigation and the duration of the vine response after the irrigation has stopped. This will permit an immediate and more detailed appraisal of vine response to weather and irrigation. The onset and duration of the water pressure in the drip line will also be placed on this graph.

Irrigation Scheduling In Terms of the Internal Hydration Level

If the level of internal hydration is the same from one day to the next, the plant was able to recharge itself from groundwater reserves. There is no need to irrigate. If the internal hydration is less that the level observed at the same time as the previous day, the plant has suffered a net loss of internal hydration. The plant was not able to recharge itself from groundwater reserves. When this trend of decreasing hydration levels reaches a predetermined level, it is time to irrigate (See the ranges show above for petiole water content levels). The desired minimum level will vary from crop type to crop type and must be determined by the operator. (See Water Content Levels of Specific Plants).

Comment on Production Applications

The primary application of the water content sensors in production agriculture is the timing and magnitude of irrigation. The rationale behind irrigation is to maintain a pre-determined water content profile over the entire season. The grower decides on the level of plant water content through the season before the season begins. For example, in the case of deficit irrigation of wine grapes the grower decides to hold the petiole water content at 60 units (nfd/mm) in June, 50 units in July, 40 units in August and harvest at 20 units. In the case of tomatoes, the grower may decide to hold the petiole water level at 70 through the season and then decrease the water level to 60 for three weeks before harvest.

Irrigation is not scheduled in the sense that water is applied in a given quantity at regular scheduled intervals. Water is applied or withheld to maintain the preset value of' water content for the particular period under consideration. For example, if on July 3, the water content level is 70 and the desired level is 65, water is withheld until the water content drops to 65. Alternately, if on July 3 the water content level is 60 and the desired level is 65, water is applied until the water content level rises to 65.

Irrigation is many times pre-emptive. If the water level is holding constant at the desired level and a heat wave is anticipated, water is applied to "ride through" the heat wave such that the plants can hold to the desired level before, during and after the heat wave. Water is an intermediate variable. This method of setting irrigation magnitude and timing lends itself to focus on the ultimate purposes of water content control such as yield, flavor or sugar level. This focus comes into play in the later stages of crop development. For example, with red wine grapes, generally flavor improves with lower levels of water content prior to harvest.

In the first step the Irrigation Manager would use the Phytogram's single point per day (minimum value) graph, to evaluate the need for irrigation. The following ranges (nfd/mm) of petiole water content levels have been developed from over 200 petiole-block seasons:

120 - 80   Ample water, no need to irrigate

  80 - 60  Sufficient water, irrigate only to maintain desired level of decline

  60 - 40   Mild water stress, irrigate to hold a desired level

  40 - 30  Strong water stress, irrigate to hold a desired level, use preemptive irrigation

  30 - 20   Severe water stress, irrigate to maintain a desired berry water content level, use preemptive irrigation

The second step would be the application of water. The Phytogram™ equipment includes a Drip Line Sensor to determine the presence or absence of water in above -surface drip lines. The output of this sensor records the exact beginning and end of irrigation. The values from the Phytotgram™ would be placed on the single point per day (minimum value) graph and the 48 point per day (every half hour) graph.

The third step would be the evaluation of vine response and determination of appropriate action.

Also see the Metabolic Activity Index (MA4) under PHYTOGRAM™.