Yet crop densities are now approaching the theoretical limit of how much food can be grown in a given outdoor area. One emerging solution is to grow multiple stacked layers of crops, referred to as vertical agriculture.[255] Vertical farms take advantage of several technologies.[256] Typically they grow crops hydroponically, meaning that instead of being grown in soil, plants are raised indoors in trays of nutrient-rich water. These trays are loaded into frames and stacked many stories high, which means that excess water from one level can trickle down to the next instead of being lost as
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