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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Citrus and Other Subtropical Products Research » Research » Publications at this Location » Publication #333643
Title: Irrigation water acidification to neutralize alkalinity for nursery crop production: Substrate pH, electrical conductivity, nutrient concentrations, and plant nutrition and growth

Author
item Albano, Joseph
item Altland, James
item MERHAUT, DON - University Of California
item WILSON, SANDRA - University Of California
item WILSON, CHRIS - University Of Florida

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2017
Publication Date: 10/1/2017
Citation: Albano, J.P., Altland, J.E., Merhaut, D., Wilson, S., Wilson, C. 2017. Irrigation water acidification to neutralize alkalinity for nursery crop production: Substrate pH, electrical conductivity, nutrient concentrations, and plant nutrition and growth. HortScience. 52(10):1401-1405. doi: 10.21273/hortsci11439-17.

Interpretive Summary: Groundwater sources used for irrigation in Florida typically contain lime. Repeated application of lime to container crops can cause potting mix pH to rise overtime, that uncorrected, can lead to leaf yellowing and reduced plant growth. To correct high levels of lime in irrigation water, growers can inject acid into their irrigation system to counteract the affects of the lime on plant appearance and growth. To study the long-term consequences of acidifying irrigation water on potting mix chemistry and on plant growth, we conducted a 52-week study. Treatments consisted of three levels of irrigation water acidification with sulfuric acid: 0%, 40%, and 80% lime reduction. The objectives of the study were to assess potting mix pH (acidity), electrical conductivity (EC), and nutrients; and plant nutrition for Thyrallis, a bushy shrub with yellow flower spikes that is grown in central- and south-Florida. Additionally, plant growth (by growth index, a measure of plant canopy volume) and plant quality (by survey), root development (by visual assessment), and leaf greenness (by SPAD, a meter that measures chlorophyll, the green pigment in leaves) was determined. Substrate analysis by the 1:2 dilution method (1-part potting mix and 2-parts water) at the end of the study was statistically significant for pH: 6.2, 5.2, and 4.7 for the 0%, 40%, and 80% lime-reduction treatments, respectively, and statistically significant for plant nutrients calcium, manganese, and zinc. Leaf nutrient levels were statistically significant for lime-reduction treatment for iron, potassium, manganese, phosphorous, and zinc. Under the conditions of the study, the 40% lime-reduction treatment was most favorable for plant production with greater growth, greener leaves, and scoring the highest rankings in a plant quality survey. The substrate analysis of the 40% lime-reduction treatment also had high levels of soluble nutrients and a pH (5.2) that fell between the recommended pH-range for the production of container nursery crops. Root growth was determined by visual assessment of the root-ball surface. Root growth for the 40% and 80% lime-reduction treatments were greater than observed for the 0% lime-reduction treatment. Therefore, based on the results of the study, the 40% lime-reduction treatment was suitable for the production of Thryallis plants. Regardless, these data demonstrate that irrigation water acidification does alter potting mix pH and nutrient concentrations, and plant tissue nutrient levels, based on the level of water acidification and duration of application.

Technical Abstract: Liming agents in irrigation water, typically associated with carbonates and bicarbonates of calcium and magnesium, 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 liming agents in irrigation water, growers can inject acid into their irrigation system to neutralize alkalinity. Therefore, a 52-week study was conducted using irrigation water, media, 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, EC, and nutrients; and plant nutrition for Thyrallis (Galphimia gracilis) to irrigation water acidification with sulfuric acid, neutralizing 0%, 40%, or 80% alkalinity [Neutralization of Alkalinity (NOA) treatments]. Additionally, plant growth (by growth index) and quality (by survey), root development (by visual assessment), and leaf greenness (by SPAD) was determined. Substrate analysis by the 1:2 dilution method at the end of the study was significant for pH: 6.2, 5.2, and 4.7 for the 0%, 40%, and 80% NOA treatments, respectively, and significant for nutrients calcium, manganese, and zinc. Leaf nutrient levels were statistically significant for NOA treatment for iron, potassium, manganese, phosphorous, and zinc. Under the conditions of the study, the 40% NOA treatment was most favorable for plant production with greater growth, greener leaves, and scoring the highest rankings in a plant quality survey. The substrate analysis of the 40% NOA treatment also had high levels of soluble nutrients and a pH (5.2) that fell between the recommended pH-range for the production of container nursery crops. Root growth was determined by visual assessment of the root-ball surface. Root growth for the 40% and 80% NOA treatments were greater than observed for the 0% NOA treatment. Therefore, based on the results of the study, the 40% NOA treatment was suitable for the production of Thryallis. Regardless, these data demonstrate that irrigation water acidification does alter substrate pH and nutrient concentrations, and plant tissue nutrient levels, based on the level of water acidification and duration of application.