Irrigation Water Acidification to Neutralize Alkalinity for Nursery Crop Production: Substrate pH, Electrical Conductivity, Nutrient Concentrations, and Plant Nutrition and Growth

in HortScience

Liming agents (LAs) in irrigation water, typically associated with carbonates and bicarbonates of calcium (Ca) and magnesium (Mg), contribute to water alkalinity. Repeated application of LA to container crops can cause media-solution pH to rise overtime, that uncorrected, can lead to a nutrient availability imbalance that may be suboptimal for plant-growth due to nutrient disorder(s). To correct high levels of LA in irrigation water, growers can inject acid into their irrigation system to neutralize alkalinity. Therefore, a 52-week study was conducted using irrigation water, substrate, and plants from a commercial nursery in Florida that has a history of poor water quality and plant production problems related to high alkalinity irrigation water. The objectives of the study were to assess substrate pH, electrical conductivity (EC), and nutrients, and plant nutrition and growth for thyrallis (Galphimia gracilis Bartl.) to irrigation water acidification. Treatments consisted of irrigation water acidified with sulfuric acid (H2SO4) to neutralize 0% (control), 40%, or 80% of calcium carbonates (CaCO3) yielding a CaCO3 (meq·L−1)/pH levels of 5 [High Alkalinity (H-A)]/7.37, 3 [Medium Alkalinity (M-A)]//6.37, and 1 [Low Alkalinity (L-A)]//4.79, respectively. Substrate analysis by the 1:2 dilution method at the end of the study was significant (P < 0.05) for pH 6.2, 5.2, and 4.7 for the H-A, M-A, and L-A treatments, respectively, and for nutrients Ca, Mn, and Zn. Foliar nutrient levels were statistically significant (P < 0.05) for alkalinity treatment for Fe, K, Mn, P, and Zn. Alkalinity treatment was significant (P < 0.05) for growth, leaf greenness (by SPAD), and quality (by survey) with the M-A treatment producing more biomass, having greener leaves, and the highest aesthetic quality value than the H-A or L-A treatments. A qualitative survey of root systems at harvest showed that the M-A and L-A treatment root systems were greater than the H-A treatment based on visual side-wall root development. These data demonstrate that irrigation water acidification does alter substrate pH and nutrients and plant tissue nutrient levels and growth over a long-term production cycle typical for nursery crops.

Contributor Notes

We thank Chris Lasser and Loretta Myers; Biological Science Technicians, USDA-ARS-U.S. Horticultural Research Laboratory (USHRL) for technical assistance; and Nancy Burrell and Elizabeth Baldwin, USHRL, for critical review of the article. This research is in support of the USDA-ARS project “Integrated Strategies for Managing Pests and Nutrients in Vegetable and Ornamental Production Systems,” project number 6034-22000-042-00D. This material is based on work that is supported in part by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2014-51181-22372, USDA-ARS-Floral and Nursery Research Initiative (FNRI), and Horticultural Research Institute (HRI).

Corresponding author. E-mail:

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    Thyrallis plants collected at the same nursery that was the focus of the study. (A) Leaves showing nutrient disorder and (B) affected plant with general chlorosis and poor growth.

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    Greenhouse temperature over the 52-week study with week-1 starting in March.

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    (A) Representative picture of experimental layout of Thryallis plants in the study. For pictures BD, treatments are from left to right: High-Alkalinity (H-A), Medium-Alkalinity (M-A), and Low-Alkalinity (L-A) at 51 (B) or 52 [(C and D) (harvest/end of the study)] weeks after the start of the study. Plants are the same for pictures BD. (B) Representative view of plant tops/canopy before plants received their final shearing. (C) Side view of root growth, and (D) bottom view of root growth.

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    Representative infloresence/flower spike of golden-yellow followers for Thryallis in the study.

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