Water Management in Horticultural Crops

Drip irrigation for different horticultural systems

1. Nursery irrigation to field grown nursery stock

• The length of the row will determine the size of tubing required. The objective is to evenly wet the row and manage the water in the root zone. Water that move out of this target zone is lost to the plant and represents a wasted resource. In most cases, it is difficult to apply all of the water needed in a day without losing water from the root zone. Hence water has to be applied more than once a day and as many times as necessary to supply the total amount required. It is called pulse irrigation. Fertilizer and other materials can be applied with safe limits and precautions.
2. Container Irrigation

• Irrigation of containers is different from field grown crops in that it has a confined space above ground subject to temperature extremes, artificial growing medium such as pine bark, excessive air movement around containers, and the force of gravity.
• Problem is, it takes the same amount of water to grow a crop in a container as it does in the field: however there is no reservoir to store the water except for the medium, which is usually very coarse. If too much water is applied at one time, or in only one place in the container, the water will quickly channel through the media and out of the pot.
• To help prevent channeling, small spray sticks are often used to spread the water over the surface of the container. However, these devices are not pressure compensating. In effect, the amount of water that flows from each one depends on the pressure forcing it. The amount of water can vary significantly down a line of pots causing variations in flow of as much as 50% from one end of a line to the other. This variation means that containers getting the least amount water have to be watered longer to satisfy their needs thereby over watering the containers getting more (higher pressure). If the grower is injecting fertilizer into his system, the problem is compounded by over applying fertilizer in some containers while not getting enough in others.
3. Greenhouse Irrigation

• There are many variations of greenhouse irrigation system layouts. The critical thing is to establish what crops will be grown. The total volume of water required is dependent on what is being irrigated. Irrigation in containers generally required relatively low flow rates per greenhouse, while propagation and bedding plants generally require overhead irrigation with comparatively higher flow rates per house.
• Control of greenhouse irrigation: Since all greenhouse irrigation applications require high frequency irrigation, automation of these types of systems using an irrigation controller is the rule rather than the exception. Depending on the specifics of the crop, the controller should offer the capability of multiple programmes, and in the case of propagation the option to programme in seconds and minutes for a given window of operation time (called a loop). It is virtually impossible to irrigate greenhouse crops efficiently without the use of automation. The cost of automation is minuscule compared to the cost of labour to effectively irrigate greenhouse crops.
i) Hanging baskets

• Hanging baskets are most effectively watered using a dripper with a flow rate 2.25 litres /hr installed on the lateral line attached to a structural member of the greenhouse. A small diameter tube is attached to the outlet of dripper. At the other end a plastic weight rests in the basket.
• The dripper should be pressure compensated and equipped with a device that allows the watering to begin instantly when the pressure rises above a certain point. It should also shut off instantly when the pressure drops to that point. All devices connected to that particular valve will start and stop irrigating at precisely the same time.
• All baskets will be watered evenly. Greenhouse growers almost always inject fertilizer through their water. The equipment described above assures 94% distribution uniformity. Each pot gets the same amount of water and nutrient. Uniformity in irrigation leads to uniformity in production. Uniformity in production means a higher value crop. The goal of the grower should be to produce as uniform a crop as is technically possible.
ii) Bench pot watering systems

• The most beneficial selection of product for this application is to choose a dripper 2 to 10 litres per hour and divide its flow rate among multiple containers (4-8). A pressure compensating device and attachment of a multiple outlet adapter to the outlet of the dripper is considered.
• Small diameter tubes are then connected to the multiple outlets of the adapter and run to each individual container. A small stake, which serves as a secondary dripper, is put into the tubing and installed in the pot. Each pot receives the same amount of water in the same amount of time. Flow rates may range from as low as 0.6 l/ hr to 1.2 l/hr per container.
4. Watering the established woody landscape
Soaker hoses

• Soaker hoses can be snaked through a landscape planting and hidden from sight with mulch. Rubber soaker hoses ooze water to provide a slow application.
Watering bags

• Watering bags are useful for newly transplanted trees located where watering is not easily done. Tiny holes in the bag allow the water to slowly seep in to the ground.
Soil watering needle

• Soil watering needles supply water directly to the root zone of the plants. The needle is inserted a number of times around the tree or shrub to assure thorough watering.