单项选择题
| Hydroponics, the science of growing
plants, in water or inert substances, represents one of the most innovative
practices in modern agricultural development. Not only does it allow greater of
the plant growth process, it permits the production of crops in hostile
infertile environments. The first widely publicized soilless gardening experiments were conducted during the 1930s. W. F. Gericke varied nutrient levels among specimens suspended in a gravel substrate (沙砾基质) to demonstrate remarkable alterations in growth. Among the findings that amazed his fellow horticulturists was the production of tomato plants over 6 meters high. The original hydroponics gardens merely consisted of plants floating in water. It was later discovered that the roots could survive in a number of media, as long as they were supplied with sufficient moisture, nutrients and oxygen. A variety of materials are used in recent versions including gravel, sand, peat, sawdust, plastics and so on. Indeed, one of the most productive methods involves suspending plants in air with a Styrofoam support and spraying them occasionally with nutrient solution to keep them moist. Many different kinds of materials are suitable for physically containing plants, yet all of these systems share one trait: the culture solution. This nutrient bath is prepared in a tank by dissolving salts which provide the necessary chemicals for plant metabolism. Constant care must be taken to assure that the sodium chloride(氯化纳)levels in the tank do not reach excessive levels as the plants draw water and minerals out of the solution. The acidity of the tank must also be maintained around 6.0 to 6.5 depending on the specific type of plants being harvested. Although soilless farming is generally more expensive than utilizing fertile land, there are many advantages that make it an important alternative to traditional practices. Herbicides and pesticides are unnecessary because of the controlled environment. The plants also need less space to grow because their nutrient uptake is significantly more efficient. The most outstanding benefit, though, is the ability to produce crops in areas with poor soil conditions or insufficient rainfall. |