A good irrigation strategy relies on control and consistency. By maintaining a consistent dryback between irrigation cycles, you create the ideal balance in your substrate. This ensures sufficient oxygen, a stable EC, and healthy root development. Remy Maat, Manager Application at Cultilene, explains how to achieve optimal dryback.

Why dryback is important
Between irrigation cycles, substrate slabs naturally dry back. This is a process that occurs in every greenhouse and with every crop. However, the amount a slab is allowed to dry back influences plant growth. Proper dryback between irrigation cycles ensures sufficient oxygen reaches the roots and keeps the EC level stable. 

The amount of dryback is a factor you can influence. It allows plants to be steered vegetatively or generatively. In general, a dryback of around 1.5% in stone wool results in neutral steering, balancing growth and fruit development.

If dryback is less (e.g., below 1%), the plant reacts more vegetatively, resulting in increased leaf area. Conversely, a greater dryback, such as 2-2.5%, triggers a generative response, promoting fruit development.

Role of the Dose Size Factor
How do you calculate the ideal irrigation volume to achieve the correct dryback? For this, you can use the Dose Size Factor (DSF). This indicates how much water you add per irrigation relative to the total substrate volume, and can give you a good indication of the drain you will be realising during the day. 

In the graph below, the optimal DSF for the second period is 25 cc, equivalent to 2.5% of the total volume. By combining this dosage size with a 2% dryback, you generate approximately 20% drainage per irrigation cycle, preventing overwatering.

Please note that this is an example. DSF and dryback vary depending on grower, region, crop, time of year and equipment. 

Why is this so important? If an irrigation cycle causes more than 60% drainage per dose, it leads to nutrient loss and root suffocation. By working consistently with the DSF and closely monitoring the dryback, you maintain control over the water and nutrient balance in the slab. This ensures a stable EC and prevents fluctuations that negatively affect plant growth.

Would you like to work with DSF and dryback yourself? The table below provides a useful overview of the drainage levels you achieve at a given irrigation size to reach the desired dryback. 

Control and consistency
A stable dryback between irrigation cycles gives you control over your irrigation process. This consistency ensures a uniform EC, consistent water content and predictable drainage in your slabs. Such stability is crucial for healthy plant growth. If shot sizes and dryback vary constantly, this can negatively impact growth.

At Cultilene, we use a 1.5% dryback as a baseline. However, certain crops and conditions may require adjustments. For instance, cucumbers often benefit from smaller irrigation volumes and slightly higher frequencies. That is why it is crucial to set clear goals at the start of the season. Define your ideal values and set your lower and upper limits for water content, EC, and dryback. This way you can adapt your irrigation strategy to the needs of your crop throughout the season.

The information provided by Saint-Gobain Cultilene has been compiled with great care and is intended solely as a guideline for the user. Saint-Gobain Cultilene therefore cannot guarantee any errors and no rights may be derived from the information or advice provided. The user himself is responsible for checking the accuracy and suitability of the information and advice for application. No commercial use may be made of the information and advice provided by Saint-Gobain Cultilene, in whole or in part, without the written consent of Saint-Gobain Cultilene.