OFA Bulletin January/February 2011 : Page 3

January/February 2011 • Number 925 accessible for more people (geographically and financially), the expansion of Garden Center Live! SM , the continued growth of Short Course, a greater presence at other industry events (domestically and internationally), and enhanced member services on our web site, among many other initiatives. It is reported that the global economy is on the upswing. But we are not yet out of the proverbial woods. Nobody really knows how the horticulture industry will endure these economic strains. There is much to be done to ensure the long-term prosperity of the industry and your businesses. Be assured that you have a partner in this effort and that OFA is committed to supporting and advancing professional horticulture. Please know that our strategic planning is not a closed system. I welcome your ideas, and you are invited to get involved with the organization. To read the strategic plan, please visit www.ofa.org/governance.aspx. Michael V. Geary, CAE Chief Executive Officer OFA – The Association of Horticulture Professionals 2130 Stella Ct Columbus, OH 43215 614-487-1117 mgeary@ofa.org Grower Understanding Irrigation Water from a Nutritional Standpoint by Bill Agro and Paul Fisher W ater quality is a key factor affecting pH and nutritional management in container-grown crops. The challenge is that irrigation water is not consistent throughout the greenhouse and nursery industry, and can differ dramatically between operations, or even from different sources within the same greenhouse or nursery (Table 1, page 4). Understanding a few technical details about water quality will help you to improve nutrient management appropriate for your own operation. and arsenate. However, under most conditions, the ions that have the greatest effect on alkalinity are bicarbonates like calcium, magnesium, or sodium bicarbonate and, to a lesser extent, carbonates like calcium or sodium. Therefore, alkalinity can be thought of as the “lime content” of the water. Alkalinity is usually measured by adding small amounts of a dilute acid to a water sample until it reaches a pH of 4.5, at which point, alkalinity is said to be 0. The amount of acid added to bring the sample to pH 4.5 corresponds to the alkalinity concentration in the water. The units used to report alkalinity are equivalents of calcium carbonate (CaCO 3 ) and the concentration is reported as per million (ppm), mg/liter, or millequivalents (meq) (Table 2, page 4). Hardness is a measure of water’s ability to form scale in pipes, produce suds from soap, or to leave spots on leaves. Like alkalinity, the units used to report hardness are calcium carbonate equivalents (CaCO 3 ). However, while alkalinity is a measure of all chemical bases in the water (bicarbonates and carbonates), hardness is a measure of the combined concentration of calcium and magnesium in the water because it is insoluble salts of ions, like calcium carbonate, that form scale. A water softener is typically used to remove hardness. What is occurring with hardness removal is that the calcium and magnesium ions are being replaced with an ion that doesn’t cause scale, like sodium or potassium. However, with hardness removal, the carbonates and bicarbonates still remain in the Continued on page 4 pH, Alkalinity & Hardness are Different Aspects of Water Quality We all think of water as H 2 O. In fact, in a container of water, a very small percentage of the water molecules break apart into H + ions (acidic hydrogen ions) or OH -(basic hydroxyl ions). When you take a pH reading, you are measuring the concentrations of H + contained in the water. The pH of a solution can range between 0 (very acidic) and 14 (very basic). At a pH of 7.0, the concentrations of H + and OH -are equal, and the solution is said to be neutral. When a solution pH is < 7.0, then the concentration of H + > OH -, and the solution is said to be acidic. When a solution pH is > 7.0, then concentration of H + < OH -, and the solution is said to be basic or alkaline (not to be confused with alkalinity). Another term often used with water is alkalinity, also known as the acid buffering capacity. Alkalinity can mean different things, but in the case of irrigation water, it is a generic measurement of the total concentration of bases contained in the water. These bases can include bicarbonates, carbonates, hydroxides, phosphates, ammonium, silicates, sulfides, borates, OF A Bulletin 3

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