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[Narrator] Listen to part of a discussion in a botany class. The professor is talking about hydroponics.
[Professor]
Although the recent interest in hydroponics may lead you to believe that it’s a relatively new idea, the  Q29
process probably originated in ancient times. In fact, the famous Hanging Gardens of Babylon may well
have been one of the first successful attempts to grow plants in water, that is, hydroponically. Early agriculture
in Pakistan and India as well as other areas throughout the Middle East included water crops,
and we also have evidence that the Egyptians were growing plants in water along the Nile... and that
was without soil. Asia and the South Pacific were prime locations for early hydroponic gardens. And, in
the Western Hemisphere, we know that the Aztecs had developed an advanced system of water agriculture
along the marshlands of Lake Tenochtitlan in the Central Valley of Mexico because, when the
Spanish arrived, they made drawings in their journals of "floating islands of trees and vegetation," in
other words, hydroponic agriculture.
Okay, well, this isn’t a history class. It’s a botany class. But I think it’s important when we’re talking  Q30
about scientific discoveries that we understand how science works. Sometimes we’re rediscovering and
refining methods that have been used for a very long time, and that’s certainly the case of hydroponics.
Through the years, it’s been called nutriculture, chemiculture, acquiculture, soilless culture, but the
current term is hydroponics, and that encompasses the modern science of growing plants without soil
by using an inert medium such as sand, peat, gravel, or... or even sawdust or Styrofoam. Of course,
you have to add a solution of nutrients.
Clearly, good soil has the nutrients necessary for plant growth, but when plants are grown without
soil, all the nutrients must be provided in another way. So, why do you think that we would go to all of
this additional effort to replace soil?
[Student 1]
Well, I think the book mentioned something about keeping the growing medium more sterile.
[Professor]
Umhum. Soil-borne diseases and pests and even weeds can be... virtually eliminated... by using a
soil alternative.
[Student 1]
So I was thinking probably you wouldn’t require as much labor, to get rid of the pests and weeds.
[Professor]
Good thought. Now tell me what you know about fertilizer and water.
[Student 2]
Oh, right. Less fertilizer and water are required per plant since they’re constantly reused, and aren’t the
results more uniform because of the highly controlled conditions?
[Professor]
Right on both counts. But probably the most important advantage is the ability to cultivate a larger number  Q31
of plants in a limited space..... Where would this be important do you think?
[Student 1]
Well, small or isolated environments or very arid climates with limited fresh water supplies probably.
[Student 2]
Or regions with poor soils, for instance, in developing countries where the weather conditions aren’t  Q32
dependable ands., and famine might... could happen.
[Student 1] Or the area may have a dense population.
[Professor] So hydroponics is limited to developing regions then.
Student 3:
I’m not sum about that. Even in highly industrialized nations, populations are growing and... and isn’t
the total acreage in cultivation dropping to accommodate the expansion of urban areas?
[Professor]
Well stated. As agricultural land is sold for development, hydroponics has become a viable option for,
well, for almost every country in the world.
Now earlier, I said that we’re often rediscovering ancient methods in science, but we’re also adapting
them by using improvements from other scientific research. In the case of hydroponics, there are
probably two modern discoveries that have supported progress in hydroponics. Okay. First, the development
of plastics... that allowed growers to abandon the old concrete beds, which were costly to construct
and problematic because... because they leached into the nutrient solution. But, plastic beds are
cheap, they’re light, and sterile... an ideal replacement for concrete. And many of the greenhouses
themselves are even built of plastic panels. Okay. The other important advancement is the knowledge
we’ve accumulated about plant nutrition. Of course, like I said, good soil has the nutrients necessary for
plant growth, but when plants are grown without soil, all the nutrients must be provided in another way.
And now we have a much better idea of what we need to use in the solution to obtain the best results.
So... all of that said, let’s talk about the lab experiment that we’ve set up here. This solution contains
potassium nitrate, ammonium sulfate, magnesium sulfate, monocalcium phosphate, and calcium
sulfate. Don’t try to write down all of that now. You can refer to your lab workbook for the list of substances  Q33
and the proportions needed for proper plant growth.
For now, just look at this diagram. The drawing in your lab workbook should look more or less like
this one. As you know, for plants grown in soil, the roots absorb water and nutrients, but they also serve  Q34
to anchor the plant. That’s why the roots of our hydroponic plants aren’t placed directly in the water and
nutrient solution. We used sterile gravel held in place by wire mesh to anchor the plants and that
allowed us to suspend the roots in the tank below. Remember, the tank contains the water and nutrient
solution. So... because oxygen is also taken in by the roots, we had to attach an air pump to mix oxygen
into the solution. Remember, a constant source of oxygen is one of the major problems with hydroponics
tanks of this kind. And you can see the way that the pump is attached to the tank.
Okay, it’s almost time for our break this morning, so I’d like you to come over to the hydroponics
area and examine the experiment close up. I’d also like you to take a closer look at this specimen of
nutrient solution. What do you notice about this? Can you draw any conclusions? Today is Day 1 for you
to record your observations on the chart in your workbook.