pH buffering of nutrient solutions with differing water quality in small-scale hydroponic systems

Abstract

Nutrient solution pH and water quality are challenges faced by small-scale hydroponic growers. The objective was to evaluate the use of the pH buffer 2-(N-morpholino) ethanesulfonic acid (MES) as an initial dose to simplify pH management in small-scale hydroponic systems, and its effectiveness within the range of alkalinity that commonly occurs in irrigation water. Two experiments tested pH buffering capacity in response to acid-base titrations, and when growing compact tomatoes (Lycopersicon esculentum) over a nine-week cycle. MES was applied at 0 to 10 mM in water and nutrient solutions at five water qualities ranging from 4 to 295 mg^.L⁻¹ CaCO₃ alkalinity. Solution buffering increased with addition of fertilizer, increasing doses of MES, and increasing water alkalinity. The MES decreased pH variability over time in all water qualities, without affecting plant growth or causing nutritional disorders. The pH of solutions without MES ranged from 4.5 to 8.0 over the growing cycle, whereas in 10 mM MES solutions it ranged from 5.7 to 7.0 for alkalinities 0 to 146 mg^.L⁻¹ CaCO₃ and reached 7.6 for 295 mg^.L⁻¹ CaCO₃. Titration of nutrient solutions after tomato growth indicates that MES acid-buffering capacity was partially consumed along the trial, which was probably the result of MES decomposition or interaction with acids and bases in solution. Results indicate that a single 10 mM MES application could be used by small-scale hydroponic growers to provide acceptable pH buffering for low to moderate alkalinity levels, but initial pH adjustment may be necessary and solution pH may still increase with high alkalinity.

Keywords:

• Alkalinity
• buffer
• Lycopersicon esculentum
• tomato
• 2-(N-morpholino) ethanesulfonic acid

Disclosure statement

No potential competing interest was reported by the authors.

Additional information

Funding

We thank Dr. Daniel Talham for his valuable comments and chemistry insights on this research. This work was supported by the U.S. Department of Agriculture-Agricultural Research Service under the Floriculture and Nursery Research Initiative #58-3607-8-725, USDA National Institute of Food and Agriculture projects multi-state NC1186 and Hatch FLA-ENH-005918. Industry funding was provided by partners in the Floriculture Research Alliance at the University of Florida (floriculturealliance.org) including nutrient analysis services provided by Quality Analytical Laboratories.