Irrigation is one of our most critical cultural practices in production of nursery crops and yet is one that we offer the least attention at most nurseries and in our research. A good thing about the water/plant relationship is that plants have evolved to tolerate extremes in water availability to account for nature's fickle schedule of irrigation. However, in the nursery BUSINESS, we do not strive just to keep plants alive. Our goal is to produce quality plants in the shortest time, using the minimum space possible with the least impact on the environment while reducing costs with efficient and effective use of our other resources. While a large segment of our industry is still made up of small family farms and plant lovers, a common comment often heard is that "the plants I like the most at my nursery are the ones that are going on the back of a truck and heading out to my customers". It is a business and the objective is not to keep plants around the nursery any longer than necessary. Our competition, production, business and marketing knowledge have increased over the years. We do not keep plants "past their time". One area we can improve on to shorten a plant's production time is to improve our irrigation practices. Many nurseries have added some automation aids over the years, primarily to reduce labor. We are beginning to see some small advances in improving our irrigation practices as a result of environmental pressures and the great motivator, "MONEY"! There are a number of hardware and software irrigation factors we can adjust, improve and maintain to increase plant growth. The design of our nursery, the media we use and the container designs can also improve our irrigation efficiency and effectiveness.

Irrigation hardware includes items that get the quality (pre-tested) water from the water source to the plants. Pumps, filters, pipes, backflow devices, emitters and pressure compensators fall into this category. A professional should design hardware so that a uniform volume of clean water reaches each plant. If you do not treat all plants within a group the same, how can you get uniformity of growth or diagnose problems when they go wrong? Again, we are not just watering plants to keep them alive, we are trying to use irrigation management to get maximum growth. Hardware needs to be maintained and tested frequently for uniformity. Replacement parts should be parts designed for the system and not ones that just fit.

Irrigation software involves the mechanisms and equipment involved for scheduling and applying the appropriate volume of water to meet the needs of the plants. This can be as simple as sticking your finger in the substrate to feel the wetness (our manual sensor) or using irrometers to electronically quantify the moisture in the soil or how fast the plant is using it. This is an area where recent research efforts at Auburn University were targeted.

We began thinking complete automation by running wires throughout the nursery with irrometers in a number of pots to measure the water loss to the atmosphere and the plant. We wanted to replace that daily water loss each day with minimal leaching. We found the irrometers were not very accurate. So, we cooperated with our electrical engineers to write a complicated fuzzy logic computer program so the computer could monitor and "learn" the variability of the irrometer instruments and make corrections. We grew a crop of greenhouse plants in the to test the technology and it did great except for needing 100 wires and our own electrical engineer to make frequent adjustments to the program. Application of this technology can be done and I am sure it will be in the future, but for now, it is a big jump from a greenhouse crop of 40 plants to a nursery with millions of plants of different species, sizes, and highly variable water requirements even within the same species and container size.

Our plan of attack now is to continue making more improvements in irrigation application and efficiency than we are currently by taking practical, economically feasible baby steps. This involves combining current technology to partially automate irrigation and make the same normal, manual adjustments to environmental conditions that you would do if you had the time to stand by the tap all day and turn it on and off. We can use timers, light, rain, wind, evaporation, relative humidity Class A evaporation pans and temperature sensors. We can also adjust the substrate and container design so that it will hold more water while still maintaining a balance of air space. We know that as light, temperature and wind increase, plants will demand more water and conversely as these factors decrease and relative humidity goes up or it rains, we must reduce our irrigation to adjust for the plants lower water needs. That is simple. The problem is time and having experienced, knowledgeable people to be monitoring and adjusting for all these factors, complicated by the large number of species and sizes of plants. We need to use our experience to calibrate the electronic aids so that they can be monitoring the environment night and day and taking our place at the on/off switch.

The first thing to adjust is the substrate and water reserve. By adding 10 to 25 percent of peat moss or coir, we can increase the total amount of water held in reserve, the easily available water and reduce the frequency of watering. Research conducted at Auburn University on red maples in 15 gallon pot-in-pot production using media combinations of 4:1 pinebark:peat and pinebark:coir and 100% pinebark resulted in a 17% and 12% increase in height in the pinebark and peat over the other two media, respectively. We thought that we could adjust the water to compensate for the lower water holding capacity of the 100% pinebark mix. But, we found that the peat or coir added more available water and possibly greater nutrient holding capacity to generate more growth with the species we tested. Other research at Auburn has also found potential increase in growth by raising container holes and reducing them in size to limit leaching and increase the water reserve. This idea was originated by Rigsby Nursery in Fort Myers, Florida (941-543-3379) where Bob Rigsby developed the EFC container and continues to see benefits from this container modification. A side benefit to the smaller raised holes is the control of rooting out in pot-in-pot production, which Dr. Patricia Knight at Mississippi State University has investigated. We are doing follow up research on these factors to verify and fine tune the results that will hopefully continue to be positive.

Changing the volume of water applied and the frequency of application can also increase available water, reduce fertilizer loss and runoff from the nursery. This cultural practice is termed cyclic irrigation. With cyclic irrigation, the normal water volume you apply at one application is divided into equal amounts and applied 3, 6 or more times a day. Research has shown that this technique will give equal or increased growth with the added benefit of reduced runoff. This practice has proven effective in many research projects and is worthy of trying at your nursery.

Glenn Fain, a graduate student at Auburn University, grew red maples in 15 gallon pot-in-pot containers under 1,3 and 6 cycle irrigation treatments at Auburn University. Red maples had a 23% and 17% increase in dry weight while receiving the same total volume of water in 3 cycles and 6 cycles, respectively over dry weight production of trees under a single application of water. Total nitrogen leached per pot was reduced by 99% in the 6 cycle treatment over the 1 cycle treatment with an obvious increase of nitrogen retention in the containers receiving 6 cycles. More available nitrogen (within safe limits) yields greater growth. Rob Trawick, who just completed his research at Auburn, reported similar increased growth with cyclic irrigation on white cedar and Arizona cypress in 3 and 7 gallon containers, respectively. The volume of irrigation applied in this research was 0.59 gallons per 3 gallon container daily (unless interrupted by ½ inch or more of rain) from April to mid June. The volume increased to 0.81 gallons until mid-July and peaked at 1.0 gallon per pot from July until mid September. The 7gallon Arizona cypress received a total application water volume during each of the above intervals of 0.63,1.0, and 1.03 gallons at each application. Volume of water applied was based on replacing moisture loss during the day and is explained below.

Future research will look at applying the irrigation at different times of the day with varying volumes to adjust for the different water demands as you go through the day. You can calculate the approximate water to add each day by watering the plants on a bright, hot day, allow for drainage to stop, then weigh the container to determine the weight at the maximum water holding capacity or "container capacity". At the same time the next day, weigh the plants again prior to irrigation. Container capacity weight minus the weight the next day in grams equals the daily water loss in milliliters. Use this as an estimate on the total volume of water to apply each day. This is basing your water needs on the extreme case of clear days and high temperatures. This volume could be adjusted with data coming from temperature, light, wind and relative humidity sensors. Applying water in smaller increments using cyclic irrigation, you increase the volume of water held in the container and fertilizers are not leached as readily. The other adjustment method is to use cyclic irrigation and monitor the amount of leaching after irrigating. You would like to minimize the total leachate to less than 15 to 20% of the total water applied. Some of the cycles in the heat of the day may not have any leaching.

If you are going to consider cyclic irrigation, (and current research points to positive results), you will need a controller or a computerized monitoring system. Controllers and timers are less expensive ranging from $200 to over $2000. There are many different irrigation jobs that you manage on the nursery including propagation and monitoring various sized containers and species of plants with inherent variability among and between species. They are also at varying stages of growth. The flexibility of a computer system may be the economic and sound business choice to manage it all. Computer irrigation management systems range from $5000 to $10,000 or more, obviously depending on the size of nursery. Two companies that offer this equipment are Q-COM in Santa Ana, California (949-837-8418) and World Wide Water, Inc., Apex, NC. (919 362-4200). These management systems allow you to take a big step towards controlling and monitoring your irrigation. Computer systems can be a big capital expenditure but no more costly than many media mixers or other equipment used on the nursery and equally or more important than these other cultural practices.

The next step is to begin to monitor the amount of water applied and keep records for future scheduling. As water restrictions continue to tighten, we will be required to measure our water use. Flow meters are added to the system to help you monitor and adjust duration and volume of irrigation. A Mini Clik or an Electronic Rain Gauge ($100) can be added to turn off the water when a critical amount of rain falls on the plants. This certainly makes sense to add one of these devices rather than irrigating automatically during a blinding rain storm or running back and forth to the valve to manually shut off the irrigation and reschedule. With an irrigation management system, if you received ¼ inch of rain, simple commands could be added to skip one or two cycles of irrigation that day. This same flexibility can be applied for temperature, light and relative humidity sensors. Our current research is evaluating the value of these sensors, individually and in concert to determine an economic, practical system to partially automate your irrigation while increasing growth or at least reducing labor and runoff into groundwater systems. The system does not replace you but it sure saves miles of running each week and a few premature gray hairs from worrying whether plants were irrigated and if it was too much or too little. With computerized systems you can train your electronic eyes and finger in the field to keep data of what is going on and to alert you if things are not going as you instructed. A deviation in the flow to the containers at a set percentage, too much or too little, signals the computer to sound the alarm or call one or several people to let them know a problem exists or it can be instructed to call every day at a specified time to let you know all stations were irrigated. So, this is not a system just for the large nurseries. It also offers peace of mind and possibly a free day or two away from the nursery for the small nursery manager.

When it comes to irrigation, almost all growers believe we can do better than what we are doing and still make it profitable to take the small steps to improve. There will be a learning curve in the beginning to fine tune your electronic finger and eyes to manage the irrigation but after you get your system up and running you will find you will have much more freedom, peace of mind and still be able to reach the ultimate objective of uniform quality plants heading out the nursery gate. Many Universities in nursery states are working on these irrigation opportunities. Stay alert as new information develops for improving your irrigation effectiveness and begin to take small steps to improve your irrigation management.

Dr. Ken Tilt is a Professor and Extension Horticulturist at Auburn University.