Most horticultural production firms either propagate or buy seed, cuttings, or tissue-cultured propagules. These propagules are planted into small cells called plugs or liners, placed under high humidity to germinate or produce roots, and are subsequently grown to a saleable seedling plug or rooted liner, which requires 4 to 6 weeks in the case of most herbaceous cuttings. The plug or liner is then transplanted into the field or landscape or into a larger container for further growth before sale. The total value of sales of propagative plant material for cut flowers, potted flowering plants, annual bedding and garden plants, herbaceous perennials, foliage, and cut cultivated greens for 2005 was $439 million, 2% above the previous year (U.S. Dept. Agr., 2006). Annual bedding and garden plants accounted for 49% of all propagative material, or $214 million. These propagation numbers probably underestimate the economic value of the seedling and cutting industry when including vegetable, woody ornamental, and fruit production.
Agriculture accounts for over 80% of freshwater consumption in the United States and an increase in water use regulations necessitates improved irrigation strategies (Weibe and Gollehon, 2006). Greenhouse propagation involves considerable application of water for control of humidity, soil moisture, and as a means to apply water-soluble fertilizer. In a typical rooting environment for vegetative cuttings, water is initially supplied by either mist emitters or automated boom watering systems to minimize transpiration loss. The amount of water required is species-dependent. For example, artemisia (Artemesia spp.), gaura (Gaura lindheimeri), rosemary (Rosemarinus officinalis), or lavender (Lavandula angustifolia) cuttings rooting performance is reduced in high-mist environments (Dole and Gibson, 2006). Excessive water application can lead to increased use of water resources and associated production costs, reduce oxygen availability in the substrate, and thereby reduce rooting percentage (Geneve et al., 2004). Improved irrigation management may help reduce nutrient, pesticide, and trace element loads in irrigation runoff to surface waters as well as leaching of agricultural chemicals into groundwater supplies (Schaible and Aillery, 2003).
Annual nitrogen (N) fertilizer application rates as high as 3600 kg·ha−1 N were estimated for chrysanthemum (Dendranthema ×grandiflorum) (Nelson, 1998) and poinsettia (Euphorbia pulcherrima) potted crops (Yelanich and Biernbaum, 1994). Much of the excess N applied in crops grown with high fertilizer concentrations and heavy leaching can be lost into the environment, depositing as much as 100 mg of nitrate–nitrogen (NO3-N) (243 mL or of effluent with a NO3-N concentration of 411.6 mg·L−1) per irrigation from a 6-inch-diameter pot into the soil profile (McAvoy et al., 1992). Soluble phosphate and micronutrients are also used more intensively per hectare in greenhouse production than in field crop production (Nelson, 1990).
A similar net nutrient supply can be achieved with either low fertilizer and leaching rates (resource-efficient strategy) or high fertilizer and leaching rates (resource-inefficient); and commercial horticultural practices vary widely (Yelanich and Biernbaum, 1993). Fertilizers applied to both stock plants and during propagation of cuttings impact successful rooting of vegetative cuttings in propagation (Blazich, 1988; Gibson, 2003; Lebude et al., 2004; Rowe and Blazich, 1999). Biernbaum et al. (1995) and Kerr and Hanan (1985) found that the majority of fertilizer salts were rapidly removed from container media after leaching of one container capacity (Biernbaum et al., 1995) or one soil volume (Kerr and Hanan, 1985). Container capacity can be defined as the total amount of water present in the container after the substrate is saturated and then allowed to drain for 1 h.
Previous research on leaching in greenhouses (Groves et al., 1998; Ku and Hershey, 1997; Argo and Biernbaum, 1996; Yelanich and Biernbaum, 1994) has focused on potted plants rather than propagation. We are unaware of research on leaching and fertilizer concentration in plug and liner trays in which the water inputs relative to substrate volume may be much higher than in large containers. Based on the variability in growing practices within the industry, management practices need to be evaluated and critical areas such as the amount of water and nutrients lost should be quantified to determine points of potential improvement. Our objectives were to: 1) quantify levels of irrigation water leached during production of liner trays in multiple commercial greenhouse operations; 2) quantify nutrient levels in substrate, tissue, and leachate of these commercial crops; and 3) compare nutrient use efficiency at each location.
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Schaible, G.D. & Aillery, M.P. 2003 Irrigation technology transitions in the mid-plains states: Implications for water conservation/water quality goals and institutional changes Int. J. Water Resour. Dev. 19 67 88
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Weibe, K. & Gollehon, N. 2006 Irrigation resources and water costs 26 July 2006 <http://www.ers.usda.gov/publications/arei/eib16/Chapter2/2.1/>.
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