Results of the University of Florida’s research on irrigation for nurseries
Reducing irrigation in nursery production has become a major issue due to increasing water shortages, periods of drought and irrigation restrictions. Up to now, most of the proposed solutions have required significant investments and they have tended to be highly technical. This article presents the results of experimental work conducted over many years at the University of Florida and Laval University in Canada for the purpose of developing a simple and pratical water conservation system.
By Soleno Textiles Inc.
Fig. 1. Partial view of the experiment at the University of Florida in 2001. Seen here is the first plot at the front of the installed capillary mat.
What are a nursery’s irrigation requirements?
Over the years, different water conservation systems have been recommended to nursery growers using overhead irrigation. This has included such sound methods as water recovery basins and micro-irrigation. Nonetheless, such systems exhibited certain limitations.
It became evident that growers needed an irrigation system that would:
- function on varying slopes and topography
- improve watering uniformity
- restrict weed and algae growth
- be compatible with overhead or drip irrigation systems
- collect and use rainwater
- work well with commonly used substrates
- be reliable, i.e. resistant to salt and herbicide build-up
- reduce watering of leaves and flowers to prevent disease.
Based on these requirements, different production systems were developed and tested (Haydu, 2002). These included micro-irrigation, flat plastic trays, and a capillary mat called Aquamat.
How were the experiments conducted?
Experiments on nursery irrigation systems were conducted at the University of Florida’s Mid-Florida Research and Education Center in Apopka, and at three grower locations in the United States and in Canada.
Two types of experiments were conducted:
A. A first set of experiments carried out at the Mid-Florida Research and Education Center compared different irrigation systems : a capillary mat system, overhead irrigation, micro-irrigation, pots in flat trays and similar containers on a woven black ground cover as a control.
All systems were irrigated nightly with overhead impact sprinklers. Plants on the control plots received 0.6 inch (1.52 cm) of water a day, those on mats, 0.25 inch (0.64 cm) of water a day against 0.15 inch (0.38 cm) for the plastic trays. Micro-irrigation received the equivalent of 0.7 inch (1.78 cm) which was the lowest amount of water that could be supplied to the plots. In the case of the trays, this amount provided each plant with the same volume of water as the control.
In other words, less water was applied to a given surface because water between the pots could be absorbed by uptake later in the day. In the case of the capillary mat system, this amount was required to ensure adequate operation of the system since this was the minimum water needed to initiate capillary rise into the medium.
A substrate made of 60% bark, 30% sedge peat and 10% sand was used. Viburnum odoratissimum and Ligustrum japonicum were grown and harvested when 92% of the plants had reached the Florida Fancy Grade (1995). Data on water use and operating, labor and variable costs were compiled. Additional production and economic details can be found in Beeson (2002) or Haydu (2002).
B. A second set of experiments compared the capillary mat with overhead irrigation for different species at different nurseries: Lake Brantley Plant Corporation (Longwood, FL), Houston Garden Center (Houston, TX) and Québec Multiplants (St-Apollinaire, QC, Canada).
The capillary mats were simply laid on the ground under the overhead irrigation systems with no special adaptation or adjustment. Irrigation was carried out normally, and the capillary mats were placed on adjacent surfaces in replicated or unreplicated designs.
What were the results?
Results of tests conducted at the University of Florida
Latest results (Beeson, 2002) showed that plant growth was superior with the capillary mat and flat trays than with with the control system (overhead irrigation). Micro-irrigation generally increased production time. The capillary mat and flat trays required less water than the other two systems to produce 92% plants of marketable size, and production time was shortened considerably (Table 1).
Table 1. Production time and water used to take two species to marketable size
Because of the accelerated growth achieved with the capillary mat and flat trays, these systems shortened production time by 4 to 11 weeks, compared to overhead irrigation and 5 to 11 weeks compared to microirrigation.
Because the capillary mat and trays were also given less water, these systems required 65 to 71% less irrigation than the control system for the trays, and 51 to 65% for the capillary mat. Microirrigation did not result in significant water savings (approx. 36 to 45%). Flat trays saved the greatest amount of water, followed by the capillary mat, but the high cost of this type of system limits its profitability at a time when water is still relatively inexpensive. A cost breakdown for materials and installation is provided in Table 2.
Table 2. Installation costs for different irrigation systems of #1 containers for a one-quarter acre (by square foot)
An important reason for the increased profitability of the capillary mat relates to the lower investment required by the capillary mat technology as opposed to trays and micro-irrigation. There is a cost for saving water, but increased growth rates offset this investment. The net profitability over 6 years was calculated based on all data collected in the field ( Fig. 2).
Fig.2. 6 years cumulative profits for Viburnum and Ligustrum with three different water-saving systems.
Based on combined Viburnum and Ligustrum profit data, the economic analysis revealed the Aquamat capillary mat to be the system with the most significant level of profitability. Next in line were the trays, followed by microirrigation, which generated considerably less profit (over 6 years of production on 0.25 acres). Interestingly, investments are offset by the accelerated growth, which results in savings for labor and supplies.
Results from field experiments in nurseries
Results at Lake Brantley Plant Corporation, Florida: The capillary mat was installed on the ground in August 2001 (Fig. 3). The mat was laid directly on the ground and no changes were made with regard to the irrigation system. The capillary mat was then covered with a commonly used ground cloth to allow walking on the mat and to protect it from sunlight. Potted azalea plants were then placed directly on the mat, grown for three months, trimmed and sold. After trimming, dry mass determinations were carried out on some of the plants.
Fig. 3. Potted Azalea plants were placed directly on Aquamat, which is covered with a ground cloth to allow walking on the plots.
The volumetric water content was measured in the pots at different times during the day. As both treatments were located on the same irrigation line, it was not possible to apply different amounts of water to the different plots. However, it was observed that the pots on the capillary mat maintained a higher volume of water than the pots located in the control area. Moreover, the higher water contents in the pots on the capillary mat corresponded to values at which water is more easily extracted by the plant. Consequently, higher yields were expected, and indeed, despite the fact that all the plants had previously been trimmed to the same height to determine their dry mass, the plants on the capillary mat had a dry mass 24% higher than the plants in the control plot (Fig. 4).
Fig. 4. Azalea dry mass and volumetric water content over the Aquamat capillary mat and the control pots at Lake Brantley Plant Corporation in the fall of 2001.
Results at Houston Garden Center, Texas: At the second location, three species were grown on the capillary mat. In this case, the amount of water applied could be adjusted separately for both treatments. All three species (Ligustrum, Nerium and Plumbago) showed superior growth on the capillary mat and had initially been trimmed to the same size as the control plants to determine their dry mass. In the case of all three species, dry mass was greater for plants grown on the capillary mat. For Ligustrum, the 14% increase in dry mass after trimming with the capillary mat was obtained using 63% less water than the control (Fig. 5). Growth increases were somewhat smaller for the other species, i.e., approximately 12 and 5% for Nerium and Plumbago, respectively.
Fig. 5. Plant dry mass and water used to grow marketable Ligustrum plants at Houston Garden Center, Houston, TX.
Results at Québec Multiplants, St-Apollinaire, Quebec, Canada: The same trend was observed at this third field experiment. Two species (Cotoneaster and Spiraea) were grown and the amount of water applied to each treatment was adjusted separately. Differences in plant growth were evident (Fig.6) with a 48% increase in shoot dry mass for Spiraea and a 101% increase in shoot dry mass for Cotoneaster on the capillary mat as compared to the control. Data on water content collected in the field confirmed that the pots on the capillary mat were watered with greater uniformity than the adjacent pots under standard overhead irrigation and that the capillary mat could effectively redistribute water on land with a slope of 3%. As well, the capillary mat used 13% less water than the control treatment. Water savings were less significant at St-Apollinaire than in Florida and Texas, possibly because the larger plants on the capillary mat had to be watered more frequently by the end of the experiment.
Fig. 6. Plant dry mass after 4 months of growth at Québec Multiplants, St-Apollinaire, Quebec, Canada.
Fig. 7. Cotoneaster plants placed on a capillary mat at Québec Multiplants, St-Apollinaire, QC, Canada.
Data from experiments conducted at the University of Florida and at different grower facilities showed that capillary mat technology and water trays saved considerable amounts of water while improving growth. In cases where the yield increase compensated for the investment required, it was more cost-effective to use a capillary mat system than microirrigation. In addition to the simplicity and versatility of the Aquamat capillary mat, the extensive research work conducted on the system confirms the environmental and economic advantages of this technology, helping growers to increase profitability by saving water.
What is this irrigation system?
Known as AQUAMAT® the Water Conservation System, this irrigation system is, essentially, a capillary mat designed specifically for the nursery environment.
For years now, standard capillary mats have been developed and widely used in greenhouses. However, when installed in the field, these mats performed poorly, because of problems such as algae and weed growth, rooting into the mat, and considerable surface evaporation under windy conditions.
To counter these problems, a special mat was designed. It consists mainly of two layers: one that redistributes water under varying slope conditions and surface topography; and a second, the evaporation lock, which acts like a valve.
This second layer allows free water (from rainfall and irrigation) to enter the mat, but will not release it, except under the nursery pots. This layer offers the additional advantage of preventing weed and algae growth between the pots.
Finally, this mat system effectively cuts irrigation volumes while accelerating plant growth.
Haydu, John J. Economic Evaluation of Alternative Irrigation Technologies for One-Gallon Container-Grown Woody Plants. Mid-Florida Research and Education Center, University of Florida, Apopka, Florida, 2002.
Florida Grades and Standard, Division Plant Industry, Dept. of Agriculture and Consumer Affairs, State of Florida, 1995.
Beeson, Richard C. Comparison of Laval University Capillary Mats to other landscape nursery irrigation systems, Mid-Florida Research and Education Center, University of Florida, Apopka, Florida, 2002.