Irrigation scheduling in a container nursery presents many challenges to water managers. One challenge is accounting for the variability in crop production conditions that exist at any given time in the nursery. It is common for container nurseries to have a wide variety of plants at several stages of production that require different amounts of irrigation water. Plants may be grown in different-sized containers ranging from small containers placed in high densities and irrigated with sprinklers to large containers (≥7 gal) placed in lower densities and irrigated with directed microirrigation, typically using spray stakes. A second challenge is accounting for the variability in the irrigation system’s ability to deliver water uniformly within the irrigated area and at a rate that is consistent from day to day. System design and reliability play a large role in this regard. A third challenge is accounting for the variability in weather conditions that affect water loss through evapotranspiration (ET) as well as accounting for rain that may reduce the irrigation requirement. An irrigation scheduling strategy that considers these variables should provide an opportunity for conserving water while maintaining profitable plant growth and quality.
LF testing monitors the amount of leachate (container drainage) that results from irrigation. The LF is defined as the amount of leachate divided by the amount of irrigation water that was applied to the container. Because LF testing measures container drainage, which is considered the undesirable result of irrigation, it also provides a direct measurement of irrigation efficiency. If LF testing is conducted on representative plants in representative areas of each irrigation zone, and testing is routinely conducted to account for changing production conditions (e.g., growth flushes, pruning, spacing), then LF testing can help account for variability in water needs throughout the container nursery. Routine leaching fraction testing coupled with irrigation adjustment to maintain a target LF was found to reduce irrigation water use 43% in a Virginia nursery (Stanley, 2012). Decreased water use led to reduced costs associated with chlorine, electricity, fertilizer, and herbicide. Other benefits of reduced irrigation amounts included better crop uniformity and fewer disease problems. Despite these promising results, routine LF testing has not been widely adopted as an irrigation management practice.
Although LF testing can be used to make intermittent adjustments to irrigation, there is potential to further improve irrigation efficiency by making real-time adjustments to irrigation based on real-time weather collected on-site. We developed a web-based irrigation scheduling program called CIRRIG (Million and Yeager, 2015) that uses real-time weather to calculate potential rates of ET that provide an index for real-time adjustments to irrigation amounts. Compared with a Florida nursery’s traditional irrigation practice of only making seasonal adjustments in irrigation run times, using CIRRIG to microirrigate a landscape plant in a trade 15-gal container decreased irrigation water use by 50% but also decreased plant growth 10% to 15% (Million and Yeager, 2019). Decreased plant growth was attributed in part to water stress that occurred despite using a target LF of 25% indicating that a target LF >25% may be required to maintain optimal growth with certain container substrates and/or irrigation systems. It should be noted that in this trial, irrigation was applied only once per day so that better irrigation water retention might have resulted if irrigation was scheduled for two or more cycles per day (Beeson and Haydu, 1994; Tyler et al., 1996). Although the results of this trial were promising, additional research was indicated to test the technology on a wider range of crops including sprinkler-irrigated plants and over greater production times.
The objective of this study was to further evaluate this CIRRIG strategy by implementing an automated CIRRIG irrigation system at a container nursery and comparing water use and plant growth of several landscape crops grown in small containers with sprinkler irrigation as well as in large containers with microirrigation. We include a brief economic evaluation of costs and benefits of the tested irrigation practice based on input from nursery staff.
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