Electrical Conductivity Levels
Different crops grow well at different levels of nutrient strength (Electrical Conductivity - EC or
CF).
It is important to control the nutrient strength to provide the conditions in the root zone which provide maximum uptake of balanced nutrition into the plant, while minimising stress.
For each crop there is a range in which the nutrient strength is optimal, providing enough nutrient for growth, but not so strong that the concentration of salts in the plant gets too high. Electronic meters are available to measure the conductivity of the nutrient solution. See Truncheon Nutrient Meter and Combo Meter.
pH Levels
It is important to maintain a hydroponic nutrient solution at a pH where the elements in the nutrient solution are available to the plant. Each element has a pH range in which its availability is maximised. The range in which most elements are available is between 6.0pH and 6.5pH for most plants but the plants will survive in a range between 5.0pH and 7.5pH. Strong acid (low pH) or alkali (high pH) conditions will upset the balance of the nutrient solution and can damage the plants.
Electronic meters are available to measure pH levels of the nutrient solution. See pH Meter and Combo Meter.
Nutrient
Nutrient - Source of Essential Elements
There are fifteen essential elements that plants feed on. The three main elements – Oxygen, Carbon and Hydrogen are absorbed from the root zone or the atmosphere. In a hydroponic system the plants rely on the nutrient solution to supply all the necessary elements for growth through their roots. The elements that are required in relatively large quantities are Nitrogen, Phosphorous, Potassium, Calcium, Magnesium and Sulphur. The remaining six elements (known as Trace Elements) - Iron, Zinc, Manganese, Copper, Boron and Molybdenum - are needed in much lower quantities.
Chelated Micronutrients
In nutrient solutions metal ions can easily form insoluble precipitates with inorganic ions present in the solution, which makes the elements unavailable to the plants and likely to cause blockages of filters and drippers in the system. The use of chelates provides an efficient and convenient way to overcome the problems associated with precipitation. The chelating agent protects the metal from reaction, keeping the metal chelates both highly water soluble and in a form which plants easily absorb.
Liquid vs Dry Nutrient
For commercial operations liquid nutrient is not usually an economic way of supplying nutrient to the grower. The majority of liquid nutrient is water and this significantly increases the freight cost of purchasing the nutrient. There is also a limit to how concentrated a liquid nutrient concentrate can be before components of the formulation come out of solution.
‘Dry’ Nutrient is usually supplied in two bags – ‘A’ and ‘B’ – to be mixed with water by the grower. The separate bags keep salts of incompatible minerals separated to avoid precipitation (a chemical reaction that forms solids that make the elements unavailable to the plants).
Mixing of Nutrient
Where nutrient is supplied in ‘A’ and ‘B’ bags, it is designed to be mixed up into two separate stock tanks of equal volume. The ‘A’ bag is to be dissolved into the ‘A’ stock tank and the ‘B’ bag is to be dissolved into the ‘B’ stock tank. These two solutions should never be mixed together in this concentrated form. Any trace elements bagged separately are to be mixed into the ‘B’ stock tank. Equal volumes of the ‘A’ and ‘B’ stock solutions are to be added to the system tank until the desired nutrient level (CF or EC) is reached.
Oxygen levels in Nutrient
Plant roots take up oxygen from the nutrient solution, therefore oxygenation of water is very important in a hydroponic system. Plant health will decline if the plants are starved of oxygen.
The design of the growing system is usually one of the biggest influences on the supply of oxygen, but methods of adding oxygen to the nutrient solution are available if there is a problem with oxygen supply.
Media
There are a number of important characteristics required in media used for hydroponics. Media must have an open structure to provide good drainage and allow air to permeate, but still have a degree of water retention. It is important that media is sterile and inert to minimise diseases and ensure good control of nutrient pH levels.
Perlite
Perlite is a natural mineral which has been heat treated. This produces a sterile, light material which is ideal for providing aeration for seeding. Horticultural grade Perlite is screened to
remove the fines, leaving granules of 2-5mm in diameter. Perlite does not have good water retention qualities and is usually mixed with Vermiculite to increase retention.
Vermiculite
Vermiculite is another natural mineral which expands on heating into a light spongy product. It can hold up to five times its own weight in water, providing a good water store for the plants. A mix of Vermiculite and Perlite gives the ideal combination of aeration and water retention and this is used for seedlings through to mature plants.
Pumice
Pumice is a light siliceous vesicular volcanic rock that is suitable for use in horticulture and hydroponics. Its porosity provides plenty of air spaces that maintain aerobic conditions around the roots while water is contained within the pores. Surface tension around the outside of the pumice particles increases water-holding capacity of the growing medium. This porosity allows free drainage minimising the risk of root rot diseases.
Neem Coir
Neem Coir is made from fibre processed from the coconut husk and powdered Neem seed cake. Neem compounds are a natural organic and eco-friendly pest repellent. The coir has a sponge-like structure with good water retention qualities.
Coco Peat
Coco Peat is made from the husk of the fruit from the Coconut Palm. It is a natural growing media made from renewable resources that has excellent water and air retention properties. The soft structure of the Coco Peat promotes fast, healthy root growth. Coco slabs are highly suitable for vegetables such as tomato, capsicum, cucumber and aubergine and promote vigorous growth. Coco slabs can also be used for ornamental plants such as roses and
gerberas.
Rockwool
Rockwool is manufactured by melting Basalt rock, spinning out fine strands and compressing into slabs. The slabs are cut into convenient sizes for various applications.
Expanded Clay
Expanded Clay Pebbles can be used for a variety of applications from flowers and vegetables through to trees and shrubs. They can be used in media beds, container or bag growing, or flood and drain (ebb and flow) systems. Clay pebbles are chemically inert, have a neutral pH, do not degrade and are clean and odourless. They are usually supplied in one of two sizes – 4-8mm diameter or 8-16mm – allowing for different root structures and control of water and
oxygen retention. The pebbles can be mixed with other media to provide the right balance of aeration, absorption and retention of nutrient solution.
Automation in horticulture
Over the past 20 years automatic controllers have been developed for a range of tasks that growers have traditionally carried out manually. With the power of computers, monitoring and control of simple aspects of growing through to control of complex environments are now possible. Growers can attend to other aspects of their business, confident in the knowledge that their systems are being monitored and controlled to optimise growth and yield.
Irrigation Control / Ebb and Flow
Simple irrigation controllers are used to switch a pump on and open solenoids in sequence on a timed basis to ensure crops are irrigated at the correct frequency and duration. These
controllers can also be used to control ebb and flow (flood and drain) benches.
Nutrient / Fertigation Controllers
Nutrient EC (Electrical Conductivity) and pH levels are critical to optimisation of crop growth. Control of these parameters will ensure that the target EC and pH levels are met 24 hours a day. A nutrient controller measures the electrical conductivity of the solution (which is proportional to the level of nutrient available to the plant) with a probe, and uses that information to determine how much nutrient stock solution needs to be added to the main tank to achieve the desired nutrient EC level. In a similar way, a pH controller measures the pH with a probe, and uses the information to determine how much pH raise or lower solution needs to be added to the main tank to achieve the desired pH level. The type of dosing system used to deliver the nutrient stock solution or pH correction solution will depend on the size and type of system. Dosing system options include gravity fed solenoids, peristaltic pumps, or in-line venturi injectors. Fertigation controllers combine the irrigation timing and nutrient control in one unit. The controller doses nutrient and pH solution to achieve the desired levels in the system tank, then controls the sequencing of irrigation of the nutrient. On larger systems the nutrient is dosed inline, as the water is pumped out to the growing system.
Greenhouse Environment Controllers
There are a number of important variables that impact crop growth inside a greenhouse.
These include:
•Air temperature
•Air humidity
•Solar Radiation
•Carbon Dioxide
•Air movement
Sensors inside and outside of the greenhouse are able to measure the levels of these variables and deliver the information to a controller. In response to these sensors, the greenhouse environment control system can adjust vent position, fans, heating, fogging, shading, lighting, irrigation frequency, irrigation nutrient levels and CO2 levels. The interactions between the variables requires an integrated approach to control, so that the control actions work together to achieve the desired result. For example heating and venting need to be carefully synchronised to control temperature and humidity without wasting valuable heat energy unnecessarily from the vents.
Data logging
The valuable information on nutrient status and greenhouse environment that is collected by the sensors for the controllers can be stored on a computer. This can be retrieved and displayed in graphical form for analysis at a later date using custom designed software. A grower can learn from previous growing history and use that information to improve crop health and yield year by year.
