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Abstract
Excessive alkalinity in greenhouse irrigation water can increase substrate solution pH, resulting in reduced micronutrient availability for plants. A spreadsheet was designed to offer a quick and practical method for calculating: 1) amount of nitric, phosphoric, and sulfuric acid required to achieve an endpoint alkalinity or pH in irrigation water; 2) the amount of nutrients added by the acid addition; and 3) acid costs. It calculates both pH and alkalinity after acidification, regardless of endpoint selected. The spreadsheet accounts for the pH dependent reaction which determines the relative percentage of each of the carbonate species ‐carbonates (CO3 2‐), bicarbonates (HCO3 ‐), and carbonic acid (H2CO3) ‐ present in the solution. In addition, the acidification calculations account for the starting pH of the solution, the alkalinity found in the initial solution, and the dissociation characteristics of the acid selected to neutralize the alkalinity. The spreadsheet was validated with six water sources from Indiana and North Carolina. Those results showed alkalinity neutralization within an acceptable range of both target alkalinity and pH. The spreadsheet provides a chemical basis for acidification and provides results useful for making grower recommendations for acid additions to irrigation water to neutralize alkalinity.
Notes
Current address: Department of Horticulture, Iowa State University, 147 Horticulture Hall, Ames, IA 50011.
Department of Horticultural Science, North Carolina State University, Raleigh. NC 27695–7609.
Journal Paper No. 14711 of the Agricultural Experiment Station of Purdue University, West Lafayette, IN 47907. The project was funded in part with a grant from the Fred C. Gloeckner Foundation.
