Cut flowers are an important agricultural crop in California. Historically, growers have used the highest quality water to irrigate many of these sensitive and non-consumable crops to produce superior flowers. In recent decades, however, there has been an increase in agricultural production overall and an increase in population. These phenomena, when coupled with diminishing sources of fresh water, continue to intensify competition for high-quality water. One solution for the agricultural industry, especially greenhouse growers, has been to use lower quality water and/or greenhouse effluents to irrigate their crops. Many growers have also found applications for saline or degraded wastewaters in their own operations that continue to allow them to produce high-quality marketable crops (Skimina, 1992). In many instances, growers can use lower quality water to produce crops of superior quality. Cut flowers, because they are non-consumable high-value crops, are ideal for a production system that uses degraded water having higher electrical conductivities for irrigation. Historically, most cut flowers have been considered to be glycophytes and were expected to have little or no salinity tolerance (Greenway and Munns, 1980). Production of crops under saline conditions does raise concerns given that salinity stress, either as a result of an osmotic or specific ion effect, can stunt growth, produce foliar injury, affect nutrient balance, impair root function, and distort flower growth (Valdez-Aguilar et al., 2009). Recent research now indicates that many cut flowers, including varieties of Matthiola incana, Antirrhinum majus, Celosia argentea, Limonium perezii, Limonium sinuatum, and Helianthus annuus, have proven levels of salinity tolerance (Carter and Grieve, 2006, 2008; Carter et al., 2005a, 2005b; Grieve et al., 2006, 2008; Monk and Peterson, 1961). Studies performed in Israel also show that cut flowers, Japanese limonium in particular, can be produced using irrigation water with electrical conductivities up to 11.5 dS·m−1 (Shillo et al., 2002). In some instances, salinity exposure has proven benefits. Height control is an important quality issue for some floral crops. For example, when chrysanthemum and celosia are grown under non-saline conditions, the flowering stems are often excessively tall and weak. With proper management, salinity becomes an environmentally friendly alternative to chemical growth retardants to restrict height and strengthen stems (Carter et al., 2005a; Lee and van Iersel, 2008; Shillo et al., 2002).
It is also important for growers to understand how different combinations of salts will affect their crops. Flower growers in coastal regions of California will find it more useful to know how their crops will respond to increases in sodium chloride, the primary salt in sea water, given that sea water intrusion of groundwater is on the rise. Growers in the Imperial and Coachella Valleys of southern California will find it more useful to understand how sulfate-based salts of magnesium and calcium, in addition to sodium chloride, will affect their crops. Much of the irrigation water in this region is derived from the Colorado River watershed and contains nutrients and salts from agricultural runoff that increase the electrical conductivity (EC) of the water (Carter and Grieve, 2008; Carter et al., 2005a).
Zinnia elegans is native to Mexico and is grown commercially as a bedding plant and cut flower. It is known for its tolerance to hot and dry conditions (Dole and Wilkins, 1999). Zinnia is also an economically important crop in the United States. Because of its general tolerance to dry and saline environments and its economic importance, we selected zinnia to evaluate as a potentially salt-tolerant cut flower crop.
Specifically, our goals in this investigation were to: 1) determine whether marketable cut flowers of two zinnia cultivars could be produced under increasing salinity in a greenhouse environment; 2) determine whether differences were found in plant growth when plants were exposed to irrigation water dominated by either sulfate- or chloride-based salts; and 3) determine leaf mineral compositions of two zinnia cultivars when exposed to saline irrigation waters differing in ionic composition.
Carter, C.T. & Grieve, C.M. 2006 Salt tolerance of floriculture crops 279 287 Khan M.A. & Weber D. Ecophysiology of high salinity tolerant plants Springer Dordrecht, The Netherlands
Carter, C.T. & Grieve, C.M. 2008 Mineral nutrition, growth, and germination of Antirrhinum majus L. (snapdragon) when produced under increasingly saline conditions HortScience 43 710 718
Carter, C.T., Grieve, C.M., Poss, J.A. & Suarez, D.L. 2005a Production and ion uptake of Celosia argentea irrigated with saline wastewaters Sci. Hort. 106 381 394
Carter, C.T., Grieve, C.M. & Poss, J.A. 2005b Salinity effects on emergence, survival and ion accumulation of Limonium perezii J. Plant Nutr. 28 1243 1257
Flowers, T.J. & Yeo, A.R. 1988 Ion relations of salt tolerance 392 416 Baker D.A. & Hall J.L. Solute transport in plant cells and tissues John Wiley and Sons New York, NY
Grieve, C.M., Poss, J.A., Carter, C.T. & Shouse, P.J. 2008 Modeling growth of Matthiola incana in response to saline wastewaters differing in nitrogen level HortScience 43 1787 1793
Lee, M.K. & van Iersel, M.S. 2008 Sodium chloride effects on the growth, morphology, and physiology of chrysanthemum (Chrysanthemum × morifolium) HortScience 43 1888 1891
Plett, D.C. & Møller, I.S. 2010 Na+ transport in glycophytic plants: What we know and would like to know Plant Cell Environ. 33 612 626
Sharpley, A.N., Meisinger, J.J., Power, J.F. & Suarez, D.L. 1992 Root extraction of nutrients associated with long-term soil management 151 217 Hatfield J.L. & Stewart B.A. Adv. Soil Sci. Vol. 19. Limitations to plant growth Springer-Verlag New York, NY
Suarez, D.L. & Simunek, J. 1997 UNSATCHEM: Unsaturated water and solute transport model with equilibrium and kinetic chemistry Soil Sci. Soc. Amer. J. 61 1633 1646
Valdez-Aguilar, L.A., Grieve, C.M. & Poss, J. 2009 Salinity and alkaline pH in irrigation water affect marigold plants: I. Growth and shoot dry weight partitioning HortScience 44 1719 1725
White, P.J. & Broadley, M.R. 2001 Chloride in soils and its uptake and movement within the plant: A review Ann. Bot. (Lond.) 88 967 988