Part3Lecture1 - Root Zone Management for Greenhouse Growers...

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1 Root Zone Management for Greenhouse Growers Introduction The cause of many plant growth problems can be traced to water quality, growing medium and nutrition. This information is designed to help you avoid problems by using a systematic approach to managing water, media and fertilizer - squirt, dirt and fert ! Many greenhouse operators are making a serious effort to reduce the amount of water and fertilizer used. With reduced fertilizer use and reduced leaching, total root zone management needs to be emphasized. Management does not need to be more complicated, just better planned and more consistent. To develop a plan requires understanding some basic principles of plant nutrition and how water, media and fertilizer interact to affect plant growth. Historical Perspective While agriculturists have known for thousands of years that plants grow best in certain soils, the specific requirements for plant growth have only been well defined over the last 300 years. The “Humus Theory” held that all plant growth came from the soil. The plant grew larger and the soil was used up in the process. An experiment was performed in which a small willow tree was planted in a carefully measured tub of soil. Only rain water was added to the soil; yet, in five years the tree’s dry weight increased to over 190 pounds. Since only a few ounces of soil were missing, the conclusion was that, contrary to the belief that all plant growth came from the soil, it must come from the rain water. It was a few years before additional experiments were done to demonstrate that, while much of the willow tree was indeed water, the majority of the plant’s dry weight comes from a gas present in the atmosphere. Once it was appreciated that the atmosphere was not just one pure gas, but was, in fact, made up of several gases the ability of plants to take in carbon dioxide gas and produce oxygen gas was demonstrated. By the early 1800s, the growth of plants came to be represented by the following formula: Green plants + carbon dioxide + water + light organic matter + oxygen As plant or greenhouse managers, a primary responsibility is to make sure proper light and temperature conditions are maintained. The greenhouse atmosphere must also have
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2 adequate carbon dioxide and oxygen and not too much water vapor (relative humidity). At the same time the root zone must be managed to provide adequate water and nutrients. Plant Growth Plant growth is primarily based on accumulation of carbon dioxide from the atmosphere. The essential nutrients derived from the soil or provided by fertilizer are a small part of
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Part3Lecture1 - Root Zone Management for Greenhouse Growers...

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