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  3. If you are tired of watering your plants every day, you might want to try growing them right in the water. And in fact this is n

If you are tired of watering your plants every day, you might want to try growing them right in the water. And in fact this is n

admin2009-06-24  47
问题     If you are tired of watering your plants every day, you might want to try growing them right in the water. And in fact this is not a new idea: People in ancient Egypt were growing plants without soil more than 2,000 years ago. Moreover, the floating gardens of the Aztecs in early Mexico are another ancient example of gardening without soil. Nowadays this technique is widely used. It is called hydroponic gardening.
    Literally, the term hydroponics means cultivating in water rather than in soil, and in fact normal soil is not used in this process. But plants are plants, and so the concerns of the hydroponic gardener are really much the same as those of any other farmer. Even when they do not grow in soil, all plants need food, stability, oxygen, and protection from disease.
    The main nutrients required by plants are nitrogen, potassium, and phosphorus. Also, small amounts of other elements are needed. In the ancient hydroponic gardens of Egypt and Mexico, the growers had to rely on minerals that occurred naturally in the water. In modern hydroponic applications, workers carefully add these important minerals to pure water; in this way, the balance of waterborne nutrients can be controlled, depending on the kind of plants being grown and on the speed of growth of the crop.
    Plants usually get stability from the soil around their roots. Obviously, water cannot provide this. Plants farmed hydroponically are supported either by growing through a mesh over the Water, or by sinking their roots into sand or pea-sized gravel soaked in water. Either way, the plants stay upright, with their leaves exposed to the sun. They need no soil because, in this system, they do not derive nutrients from the medium that gives them stability.
    Oxygen is another essential requirement. The roots as well as the leaves of all plants must be able to breathe. If insufficient oxygen reaches its roots, a plant will die. To fulfill this need, hydroponic farmers usually keep the nutrient water flowing all the time. As the water circulates, it is aerated by splashing from one container to another: The splashing process increases the amount of absorbed air in the water.
    Finally, plants need a healthy environment. Especially when plants of the same species are grown close together, there is a real danger that diseases may spread quickly. A very clean growing medium will reduce this risk. Soil, the natural planting medium, may contain many harmful diseases or pests, but hydroponic gardening does not use soil. Starting with pure water and clean sand or gravel, the hydroponic gardener avoids many uncertainties.
    In these ways, hydroponics can overcome important agricultural challenges. For instance, hydroponic farming is able to produce worthwhile crops in regions where the soil is too poor for ordinary gardens, or where the supply of water is too scarce for normal irrigation. Also, even in fertile areas, hydroponic greenhouse makes it possible to cultivate small areas extremely densely: This can be very profitable during winter in cold climates, such as Canada or the Northern United States. Such considerations may not have mattered to the ancient Egyptians or Aztecs, but they are the basis of a thriving hydroponics industry today.
选项 A、Hydroponic gardening is ideal for locations where water is too scarce for normal irrigation.
B、Hydroponic gardening solved the problem of plant stability.
C、Hydroponic gardening makes it possible for plants to be grown inside in countries with a cold winter.
D、Hydroponic gardening is not only a very old technique but also a very modern one with great future potential.
答案D
解析
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