**4. Soilless culture technologies**

#### **4.1 Plant density**

Out-of-season strawberry cultivation requires considerable investments in shelter from typical winter weather patterns and events, such as rain, hail and limiting low temperature. To compensate with these expenses, the crop productivity must be significantly boosted. A major means to achieve this goal is to substantially increase plant density.

In the traditional soil-cultured strawberry, plant density ranges from eight to nine plants m−2. Within this range, plant density is determined by cultivar characteristics; however, the boundaries of this range are defined by aboveground inter-plant space considerations, such as light interception and mutual shading, and by the space necessary for technical operation (spray, harvest, etc.). In fact, in soil-grown strawberry, like in other cover crops, the canopy volume tends to be rather bi-dimensional, with the upper foliage layer receiving most of the light while shading the lower layers.

*Winter Strawberries Production in Greenhouse Soilless Culture under an Arid Climate… DOI: http://dx.doi.org/10.5772/intechopen.104390*

This canopy structure escalates the risks of plant diseases due to poor ventilation and proximity to the soil.

The transition of strawberry cultivation from soil to soilless cultures have significantly mitigated these constraints. Shifting strawberry cultivation to the three-dimensional space provides significantly higher plant density, enhanced light interception, and better aeration to larger canopy parts for longer time periods. As a result, crop productivity is expected to substantially rise, and the probability and severity of diseases - to decline.

Different approaches and technologies of soilless culture have been developed and examined in strawberries for decades, since the 1970s [17]. In this chapter, we describe the current perception and the recent design of strawberry soilless culture in southern Israel. It should be stated, however, that the technology is consistently 'under construction', as further enhancement is steadily sought.

#### **4.2 Eye-level hung crop**

The traditional cultivation of soil-grown strawberry is a labor-intensive crop, as fruit harvest requires daily-long hours of bending. Thus, lifting the strawberry culture from the ground closer to the workers' hand-reach brings significant ergonomic advantages easing harvest and other farming activities, which may appeal seasonal workers. One way to do so is placing the growth media containers on fixed shelves along the row, a method which requires an additional costly construction. An alternative solution, broadly accepted in Israel, is the eye-level hung system, in which the growth media containers are hung along the row using the existing greenhouse construction plus some accessory cables. This way, the system height is more versatile and can be adjusted once in a while to the average workers' height. Additionally, the ground below remains free or can be used for a secondary shade crop. Another advantage is the relatively flexible distance between rows; while a distance of 65 cm was found optimal for light interception, it can be temporarily and locally modified to facilitate ad-hoc workers' convenience. The hanging system should be designed to generate the uninterrupted slope (2.5%) required to guarantee a satiated water drainage. Therefore, the system height is about 1.9 m at the beginning of a 20 m long row, and ends at about 1.4 m aboveground.

#### **4.3 System design**

Designing the soilless culture system must obey several principal prerequisites, as follows: adequate rhizosphere space; minimal weight; rigid structure; efficient drainage; and, optimal plant positioning. In addition, the growth medium properties must be light (low self-weight when dry), chemically neutral and stable, well-aerated with adequate water retention and rapidly drained. These principles ensure optimum canopy and root development and function, provide crop uniformity, and prevent technical failures, all of which are essential for high and stable crop performance throughout the growing season.

The soilless system described here is comprised of two major elements: a rigid plastic support gutter (carrier), and a growbag—coir (compact coconut fibers) wrapped by a plastic sleeve. The gutter profile is designed in a wide U shape (11 × 5 cm), with a special mid-bottom drainage duct (**Figure 4A**). The upper edges of the vertical walls form a narrow wing; holes drilled every 1 m serve for hanging the gutter on cables attached to the greenhouse structure (**Figure 4B**). The gutters are supplied in 5 or 6 m long units that are attached (using special adaptors) in a slope

**Figure 4.** *Descriptive pictures of the hung soilless strawberry culture. A: Gutter system profile; B: growbags and drip line.*

(~2.5%) to allow the continuous flow of the drainage water. The growbag packages, 1 m long each, are perforated in the bottom side to allow drainage, while two holes in the upper side, one at each longitude edge, allow the insertion of the drip irrigation pipeline through the package and above the coir throughout the row (**Figure 4A**). On delivery, the coir medium is dry, compressed, and a bit hydrophobic. For priming, the growbags are soaked in water until fully swelled, mount well above the gutter's walls, and the growth medium completely fills the growbag. As a result, the growbag profile gets a trapezoid shape. Eleven or 13 planting holes per meter are located in a zigzag manner on both sloping sides of the growbag (**Figure 4B**).

This plant positioning in the space generates a density of 170,000–200,000, compared to 60,000–80,000 plants ha−1 in field-grown strawberries. Furthermore, the fruit quality is enhanced due to the improved environmental conditions surrounding the plant canopy and fruit, including better light interception, reduced humidity, and a significant reduction in saprophytic diseases such as botrytis and aspergillus.
