For this reason, hydroponics will probably be a major part of any space settlement.
Hydroponics uses several culture techniques. The most practical commercial method is subirrigation, in which plants are grown in trays filled with gravel, cinders, or other coarse materials and periodically flooded with nutrient solution. The solution is allowed to drain off after each flooding and may be reused as long as sufficient minerals remain in it. Another technique is called the water-culture method, and is used widely for botanical experimentation. A common kind of water culture consists of glazed porcelain jars filled with solution; the plants are placed in beds of glass wool or similar material that are supported at the surface of the solution. Roots of the plants penetrate the beds and remain in the solution. The least exact method, commonly called the slop method, is the easiest to operate. Coarse, clean sand is used in place of soil, and nutrient solution is poured on the sand in approximately equal amounts at regular intervals. A refinement of this practice is the drip method, in which a steady, slow feed of nutrient is maintained. Excess nutrient solution is allowed to drain off in both slop and drip methods.
Hydroponic culture methods are being used successfully to produce plants out of season in greenhouses and to produce plants in areas where either the soil or the climate is not suitable for the crop grown. During World War II, for example, several U.S. Army units successfully produced vegetables hydroponically at various overseas bases. In the 1960s hydroponic farming developed on a commercial scale in the arid regions of the United States, particularly in Arizona. In other arid regions, such as the Persian Gulf and the Arab oil-producing states, hydroponic farming of tomatoes and cucumbers is under way; these countries are also researching an additional group of crops that may be grown by this method as they have limited arable land.
Two 50 minute periods (for construction), then 3 weeks part time (for observation).
Advance Preparation Time
If you wish, you can build a system ahead of time to show the students what they will be doing.
Each student should read What is hydroponics? at the beginning of this page.
Have the students split up into groups (minimum of 3 people, actual size will depend on how much material is available), and build a hydroponics system. The nutrient solution can be purchased at a hydroponics supply store. They should be listed in the yellow pages. Or you can make your own. Once the system is built, plant the lettuce seeds and let them grow. For comparison, cut a 2-liter soda bottle in half and fill it with soil. Plant some lettuce seeds in there too. Make some small holes in the bottom of the bottle and place it in a pan. This way the water can drain out. For realism, try to get a grow light so you can grow the plants with artificial light. This will simulate growing the plants in a space settlement, where sunlight may be hard or impossible to get.
As the hydroponic and soil lettuce plants grow, have each group students test their hydroponic system every day. The students should use some pH paper to test the pH of the nutrient solution. Note the general appearance of the plant (green? yellow?), and measure the length of the leaves and height of the plant. The students should record their observations for later use.
After three weeks (or whenever the lettuce plants have grown sufficently) have the students take their plants out of the system and weigh them. The leaves should be separated from the roots and allowed to dry before weighing. Do the same to the lettuce that grew in the soil. In general, dry mass is the best indicator of plant growth success.
Have each group compare their data with the others. Have them make up graphs of their data and write an analysis of how their plants compared to the plants grown in soil and to their peers. Hopefully, the hydroponically grown plants will have completely outgrown the lettuce grown in soil.
Author: Thomas Beatty