A NOVEL-APPROACH TO CALCULATE ACID ADDITIONS FOR ALKALINITY CONTROL IN GREENHOUSE IRRIGATION WATER

Excessive alkalinity in greenhouse irrigation water can increase subst rate solution pH, resulting in reduced micronutrient availability for plants. A spreadsheet was designed to offer a quick and practical meth od 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 co sts. It calculates both pH and alkalinity after acidification, regardl ess of endpoint selected. The spreadsheet accounts for the pH dependen t reaction which determines the relative percentage of each of the car bonate species carbonates (CO32-), bicarbonates (HCO3-), and carbonic acid (H2CO3) - present in the solution. In addition, the acidification calculations account for the starting pH of the solution, the alkalin ity found in the initial solution, and the dissociation characteristic s of the acid selected to neutralize the alkalinity. The spreadsheet w as validated with six water sources from Indiana and North Carolina. T hose results showed alkalinity neutralization within an acceptable ran ge of both target alkalinity and pH. The spreadsheet provides a chemic al basis for acidification and provides results useful for making grow er recommendations for acid additions to irrigation water to neutraliz e alkalinity.