Principles of Irrigation Management Pt. 2

Water Requirements

Experience and good judgement are essential in determining how much and when to irrigate under any particular set of conditions. Generally, plants should be watered prior to wilting, and the medium should not be allowed to dry out excessively between waterings. The amount of water required by container grown plants, and the frequency of irrigation depends on the water holding capacity of the potting medium, amount of water already present in the medium, size of plant and container, species of plant, temperature, humidity and wind speed.

Controlling irrigation is important because too little water will retard plant growth and reduce quality, while too much will leach fertilizers and reduce aeration. Typically, container grown plants, under full sunlight, require daily watering when mature. However, during cloudy and/or cool weather, less frequent watering is usually adequate. Growing media with lower water holding capacities will require more frequent irrigation. When 35% to 50% shade is supplied (by either polypropylene or lath) irrigation frequency can be significantly reduced. The amount of water to apply at any irrigation depends on the amount moisture required within the container, the amount deflected by the plant canopy which is lost between containers when overhead sprinklers are used, and the portion evaporated during application. Generally, small plants that do not cover the container receive most of the water applied with sprinklers, while up to 50% may be deflected by the canopy of large plants. Normally the amount of water applied at each irrigation should bring the water content of the growing medium back up to 70-80% of container capacity. In the Charlotte area, contact a Charlotte irrigation expert to discuss your current water requirements.


Irrigation Systems

Key components of any irrigation system are the well, pump, and proper size main and lateral lines. Frequently these components are undersized for the area to be watered, and serious inefficiencies occur. Since proper engineering of a watering system is necessary, it is important to carefully determine the area to be irrigated with consideration towards increased capacity. Overhead sprinkling is one of the most commonly used methods of irrigating greenhouse crops. Other irrigation methods include drip or trickle and subirrigation. General information on each of these systems follows, with mention of some of the major advantages and disadvantages associated with each method. If you are interested in having a Charlotte irrigation system installed, contact a Charlotte irrigation company today!


Overhead Irrigation

This method of application has relatively low initial and maintenance costs. A major drawback, however, is uneven distribution of water. This becomes a much more serious problem when the system is also used for application of fertilizers, herbicides and pesticides. Another negative aspect of overhead irrigation is that it promotes the development and spread of foliar diseases. Efficiency of overhead sprinklers is influenced by type of spray head, spacing, and wind velocity. Fixed spray heads are best for smaller areas where they are protected from wind, and they are most satisfactory for smaller containers.

Rotating impact heads supply water with considerable force. This is desirable to obtain wide coverage, but the plant's top may deflect some of the water, causing it to fall outside the container rather than enter the growing medium. Rotating sprinkler heads are best for larger container sizes and provide satisfactory coverage in calm wind conditions. Whirling, rotating sprinklers, of various designs, provide excellent coverage but the small water droplets may not penetrate when plants have a canopy over the growing medium surface. This type sprinkler operates best in protected locations.


Drip and Trickle Irrigation

Recent advances in design of small low-cost plastic tubing provide an excellent method of watering individual
containers. This system is expensive to install, but will provide irrigation to individual containers without wetting the foliage. Several types of irrigation are available which deliver various volumes of water. Most drip systems operating at pressures varying from 40-60 ppi. become clogged bacause of the high calcium and magnesium levels in most irrigation waters, as well as from growth of algae and/or bacteria within the tubes. When small diameter tubing is used, water treatment (i.e. filtering) is desirable. These systems can also be used for injecting fertilizer and application of systemic insecticides and eeefungicides.


Sub-Irrigation

This method is frequently used for field grown crops where hardpans exist near the soil surface, but only a few nurseries use subirrigation for containers. Although this method of irrigation provides desired amounts of water, construction of beds/benches to hold water can be expensive. Another disadvantage of subirrigation is the continuous sheet of water which can provide a carrier for root rot organisms. Continuous capillary watering may also lead to salt build up in the media.

source: Texas A&M