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Title: Hypersensitivity of Ranunculus asiaticus to salinity and alkaline pH in irrigation water in sand cultures

Author
item VALDEZ-AGUILAR, LUIS - U.S.SALINITY LAB
item Grieve, Catherine
item Poss, James
item MELLANO, MICHAEL - MELLANO & COMPANY, CA

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2008
Publication Date: 2/1/2009
Citation: Valdez-Aguilar, L.A., Grieve, C.M., Poss, J.A., Mellano, M.A. 2009. Hypersensitivity of Ranunculus asiaticus to salinity and alkaline pH in irrigation water in sand cultures. HortScience. 44(1):138-144.

Interpretive Summary: Ranunculus asiaticus is a member of the buttercup or crowfoot family (Ranunculaceae) and related to peonies, acontiums, aquilegias and anemones. This herbaceous perennial plant is grown as a field crop and produces elegant flowering stems 18 to 24 inches tall which are widely used in the florists’ trade. Ranunculus is propagated by the tuberous roots and these ‘bulbs’ also have a high market value. Recently growers have become aware that, although the quality of the flowering stems remains high, the viability of the roots has deteriorated and percentage of new plants from the bulbs has decreased. The question has arisen concerning the connection between bulb quality and the use of municipal treated wastewaters for irrigating ranunculus fields. To gain better insights into the effects of degraded waters on ranunculus production, experiments were conducted in 24 greenhouse sand tanks at the U. S. Salinity Laboratory, Riverside, CA. Saline irrigation waters were prepared with electrical conductivities 2, 3, 4, and 6 dS/m. Ranunculus seedlings in 12 tanks were irrigated with these solutions adjusted to pH 6.4; seedlings in the remaining tanks were irrigated with solutions of the same composition adjusted to pH 7.8. Plant growth and quality decreased slightly with the first increment of salinity (3 dS/m), but continued to decrease as salinity increased. Irrigation waters at the higher pH level (7.8) were even more detrimental to plant yield and quality. Bulb weight decreased in response to both salinity and high pH. The following season bulbs from plants grown at 3 dS/m sprouted as well as those grown at 2 dS/m, but the sprouting percentage of bulbs grown at 4 and 6 dS/m was low. This study illustrates that Ranunculus is sensitive to low quality waters, but the results do not completely explain the effect of salinity on the resprouting ability of the bulbs. Further planned research will address the effects of other irrigation water contaminants that may play a role in bulb vigor.

Technical Abstract: Ranunculus, grown as a field crop in southern and central coastal California, is highly valued in the cut flower and tuberous root markets. Concerns regarding the sustainability of Ranunculus cultivation have arisen when the plantations are irrigated with municipal-treated waters. Although cut flower quality is not affected, viability of the tubers may be compromised by the recycled waters. A study was initiated in greenhouse sand tanks to evaluate the effect of saline irrigation waters, with and without pH control, on the growth of plants and tuberous roots of ranunculus. Treatments consisted of four nutrient solutions with increasing concentration of Ca2+, Mg2+, Na+, SO42-, and Cl- to meet an EC of 2, 3, 4, and 6 dS m-1 and pH = 6.4. The 3, 4, and 6 dS m-1 solutions were replicated with uncontrolled pH and over the experimental period averaged 7.8. Ranunculus cultivars ‘Yellow ASD’ and ‘Pink CTD’ were transplanted and irrigated twice daily with treatment solutions. Plant growth of both cultivars was severely decreased as EC increased from 2 to 3 dS m-1, and high pH caused additional growth reduction. The number of flowering shoots, number of flowers per shoot, shoot length, and flower diameter also significantly decreased. Tuberous root biomass accumulation was also markedly affected by increasing salinity in irrigation water. Tuberous root weight of ‘Yellow ASD’ and ‘Pink CDT’ decreased 82 and 89%, respectively, when irrigated with EC = 6 dS m-1 waters. High pH of irrigation water was associated with a significant decrease tuberous root weight. Sprouting percentage of tuberous roots significantly decreased when plants were irrigated in the previous season with waters higher than 4 dS m-1. Nutrient analysis of flowering shoots showed a significant decrease in tissue Ca, K, total-P, total-S, and Zn concentrations as EC was increased, while Na and Cl concentrations significantly increased. Irrigation with water of pH 7.8 was associated with a significant increase in Mg, Na, and Cl tissue concentration.