Outdoor production of plants in containers requires frequent irrigation to compensate for the limited water storage capacity of confined substrate volumes (Beeson, 2007; Warren and Bilderback, 2005). Frequent irrigation of container-grown plants places great demand on water managers to apply water efficiently at each application to avoid excessive leaching. This is particularly true for microirrigated, spray-stake production in which the water application rates (e.g., 15–40 cm·h−1) are typically 10- to 25-times higher than for those of sprinkler-irrigated production (e.g., 0.8–1.5 cm·h−1). Although cyclic irrigation is a common practice to improve water retention of microirrigated container substrates (Beeson and Haydu, 1995; Karam and Niemiera, 1994), scheduling irrigation in multiple cycles with shorter run times results in fractions of 1 min being the difference between supplying an adequate amount of water vs. an excessive amount (Million and Yeager, 2019).
One measure of irrigation efficiency is the LF, which is the amount of leachate divided by the amount of water applied to the container. If sufficient water is being supplied to sustain plant growth, then an irrigation schedule that maintains a lower LF will use less water and result in less leachate. Nambuthiri et al. (2017) used an on-demand sprinkler irrigation schedule that reduced the LF from 25% to 17%, resulting in a 35% reduction in irrigation water applied and a 65% reduction in leachate volume. Tyler et al. (1996) found that reducing the LF from 46% to 31% reduced the irrigation volume by 49% and leachate volume by 63%. Irrigation management that targets a low LF with routine LF testing significantly reduced water use at a container nursery (Stanley, 2012). Compared with the nursery’s traditional irrigation practice, irrigation adjustment based on routine LF testing reduced irrigation volumes applied during six of seven nonreplicated trials at a Central Florida container nursery, with greater water savings for microirrigated vs. sprinkler-irrigated crops (Million and Yeager, 2019). Routine LF testing targeting a LF of 20% vs. 40% reduced the irrigation volume 28% during each of two experiments without affecting plant growth (Million and Yeager, 2020).
Reducing the volume of leachate has been shown to reduce leaching losses of applied N and P from containers. Tyler et al. (1996) reported that the N leaching loss was reduced 53% after 55 d and 19% after 100 d when the leachate volume was reduced by 63%. Warsaw et al. (2009) found an irrigation schedule that reduced the leachate volume by 66% to 79% also reduced NO3–N leaching by 38% to 59% and P by 46% to 74%. During a column leaching study, Niemiera and Leda (1993) found that increasing the leaching fraction from 20% to 40% increased N leaching by 61%. Fare et al. (1994) reported that reducing sprinkler irrigation from 1.3 cm/d to 0.6 cm/d reduced the leachate volume 75% and leachate NO3–N 36% to 46%; plant growth was unaffected. These aforementioned studies, except for that by Tyler et al. (1996), involved small containers (≤3.8 L) and sprinkler irrigation. Surprisingly, the effect of irrigation schedules on fertilizer N and P leaching during plant production in large containers with microirrigation has not been well-investigated (Zhu et al., 2005).
The objective of this study was to evaluate the impact of irrigation schedules that target a low or high LF on irrigation water applied, plant growth, and N and P leaching during the production of container-grown landscape plants with spray-stake microirrigation.
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