Planning and Monitoring of Irrigation and Fertilization in Container Plants

Regular weekly analysis of emitter water and drainage water is essential for monitoring the normal growth container plants. In this review, the necessary steps for planning and monitoring irrigation and fertilization are outlined.

SAMPLING IRRIGATION WATER AND DRAINAGE

It is advised to sample water from at least one location per irrigation valve. The sampling location should represent the plot controlled by the valve, but choosing the right sampling location can be difficult if the plot is heterogeneous (for example a plot which contains plants with different water consumption or in different growth stages).

Sampling from a location which represents the “average” water consumption may not be the answer, and it is important to take into account the sensitivity of specific plants to water excess or to salinity.

For better monitoring, it is recommended to sample from the same locations every week. This allows you to follow trends and changes.

After choosing the sampling location, the irrigation should be scheduled according to two parameters: the irrigation interval and water amount, in this order.

IRRIGATION INTERVAL

Irrigation interval is determined based on water consumption of the plant, container volume and substrate properties, considering the plant sensitivity to moisture.

Here are two examples: Plant A consumes 400 ml/day, the container volume  is 2 liters and the substrate can hold 60% available water. Therefore, the interval between irrigations should not exceed 3 days:

0.6 *2 / 0.4 = 3 days.

Plant B also consumes 400 ml/day, but the container size is 1 liter and the substrate can hold 30% available water. The longest irrigation interval for plant B is 0.3 * 1 / 0.4 = 0.75 days. Therefore, more than one irrigation per day is required.

DETERMINING THE WATER AMOUNT TO APPLY

In order to prevent salt accumulation in the substrate, it is very important to let water drain from the bottom of the container.  Too little drainage will cause salinity buildup in the substrate, while too much drainage might cause leaching of nutrients from the substrate and nutrient depletion.

For practical reasons, the drainage is expressed as percentage of the volume of water applied to the container. For example, if you apply 1 liter of water and drainage volume is 300 ml, the percentage of drainage is 30%.

15-60% drainage is an acceptable range in most growing media and the appropriate percentage is determined according to the plant tolerance to salts, growing media properties, applied fertilization schedule and the grower’s experience.

Practically, the drainage percentage is determined by simple field tests, such as testing EC, pH, nitrate and chlorides both in the irrigation water and drainage water.

Once the drainage percentage is determined, it can be used as a working premise. The amount of water that should be applied in each irrigation, is the amount of water that will result in this percentage of drainage.

The parameters mentioned above should be tested at least once a week, in order to get indications of the processes taking place in the substrate, such as changes in the pH, salinity buildup, deficiencies etc.

Here is an example for a convenient table for tracking the data:

Valve	Drip	Drain
EC	pH	NO3	Cl	Volume	EC	pH	NO3	Cl	Volume
A
B
C

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