Unit 2
Topic 5-Lesson 1: Agricultural Science I
Photosynthesis: One of the most important reactions in the body
o
Plants take up carbon dioxide, water and produce oxygen plus all of the chemicals that
make up the plant
o
Important for us because we eat plants, we eat meat (which grows from plants)
o
Agriculture is based on photosynthesis
Farming
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Around 50 years ago, about 70% of the world was involved in farming
o
Today, only about 2% even though the population has grown
o
Conventional agriculture around the 1800’s was not able to fulfill the needs of people
o
It is possible today to eat better than anyone has in history
o
People worry about some of the agricultural methods used today
Pesticides
o
Are designed to kill pests and weeds and fungi
o
Not clear cut as to whether these chemicals affect us
GMOs
o
A lot of people want to end this without really looking at the facts
o
By about 2050, population will be 10 billion. We will have to use fertilizers and pesticides
to produce enough food
Organic agriculture
o
Uses manure as fertilizer. It decomposes and releases various nutrients that are needed
for the growth of crops. But there is not enough manure in the world to sustain all of the
crops.
History of fertilizer
o
Justus von Liebig back in the 19
th
century asked “what is it really in manure that allows
for crops to grow?”. He did a chemical analysis and figured out that there were various
kinds of nutrients that were needed. He grew crops and took away nutrients to see if the
plants would survive.
o
Concluded there were four major necessary nutrients:
Nitrogen
Phosphorous
Potassium
Various other elements in smaller amounts
o
Fritz Haber in the 19
th
century made developments in fertilizers move very quickly.
Found a way to combine nitrogen and hydrogen to make ammonia. Nitrogen is one of
the most important components, and at that time ammonia could not be made
synthetically.
When you buy fertilizers there are 3 numbers on the label that represent the ratio of nitrogen to
phosphorous to potassium because different plants require different ratios.
o
Liebig was the first to discover this
Ammonia
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Sometimes pumped directly into the soil
o
Mostly combined with nitric acid to form ammonium nitrate, one of the most widely
used fertilizers in the world because it provides a good source of nitrogen.
o
Problems with ammonia nitrate:
Caused explosion in Oklahoma City
Slowly decomposes to yield nitrous oxide (laughing gas), which is a greenhouse
gas which prevents heat loss in the atmosphere and contributes to greenhouse
effect like carbon dioxide
Using fertilizers, you don’t really need soil
o
William Gericke first had the idea of soilless gardening in the 1900’s.
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