Re: what are the chemicals in soil? What is nitrogen, sulfur , and phosphorus?

Nitrogen, phosphorus and potassium are the mineral nutrients required by all 
plants that are usually required in the greatest amount and most often applied 
in fertilizers. The three numbers on a fertilizer container, such as 10-15-20, 
represent the percent by weight of nitrogen, phosphorus pentoxide (P205) and 
potassium oxide (K2O). 

Nitrogen in fertilizers may occur in several forms, such as nitrate (NO3-), 
ammonium (NH4+), urea [CO(NH2)2] or an organic form such as a protein. In the 
soil, nitrate and ammonium are the two forms of nitrogen absorbed by plant 
roots. Nitrogen is an essential part of proteins, nucleic acids and 
chlorophyll.

Phosphorus is absorbed by the plant as phosphate ions, HPO4-2 and H2PO4-. 
Phosphorus is part of ATP, cell membranes and nucleic acids such as DNA. 

Sulfur is also required by plants and is absorbed by plants as sulfate (SO4-
2). Sulfur is found in proteins.

The soil solution also contains a variety of other essential mineral nutrients 
such as iron (Fe+3), magnesium (Mg+2), calcium (Ca+2), boron [B(OH)3], 
manganese (Mn+2), copper (Cu+2), zinc (Zn+2), chlorine (Cl-) and molybdenum.  

The word hydroponics was originally coined in the 1930s by Dr. William 
Frederick Gericke of the University of California at Berkeley. He defined 
hydroponics as the growing of terrestrial plants with their roots in a mineral 
nutrient solution for crop production. Prior to Gericke, solution culture was 
used just for plant research. However, the definition of hydroponics is often 
broadened to include growth of terrestrial plants with their roots in an inert 
medium such as sand, gravel, sawdust, peat moss or perlite, rather than soil. 
Regardless of the definition, hydroponics involves use of a mineral nutrient 
solution such as a Hoagland solution.

The first written record of growing terrestrial plants in water dates to 1627 
in Englishman Sir Francis Bacon's book Sylva Sylvarum. Bacon barerooted 
several different plants, including a rose, and found they survived in water 
for up to three months. Several investigators tried water culture of plants in 
the 1600s such as Robert Boyle, Thomas Browne and Robert Sharrock.

Englishman John Woodward is sometimes credited as the first to have a 
hydroponics-type experiment because he grew spearmint in water sources of 
varying purity in 1699. Woodward found plants grew better in water that 
contained small amounts of soil or suspended solids. 

The Germans Julius Sachs and Knop developed plant solution culture as a 
research technique in the 1860's. Solution culture became a standard technique 
for plant mineral nutrition research and has been used by numerous plant 
researchers and is still often used today. It is the technique used to 
determine which mineral nutrients are essential.

Gericke sensationalized hydroponics in the 1930s and was was either fired or 
quit his university job because he refused to reveal his secrets to a public 
eager to use hydroponics to get rich. The people who sold hydroponic products 
to an uniformed public were the only ones to get rich. Two other Berkeley 
scientists, Dennis Hoagland and Daniel Arnon, wrote a famous booklet that 
debunked Gericke's exagerations. Many of Gericke's exagerations about 
hydroponics still persist today. Be aware that hydroponic equipment suppliers 
often hype hydroponics to promote sales.

Many histories of hydroponics mention that ancient peoples such as Incas, 
Egyptians and Babylonians practiced hydroponics but that is a myth. The key to 
hydroponics is the use of a mineral nutrient solution either with or without 
an inert rooting medium. Ancient peoples had no understanding of mineral 
nutrient solutions so they did not use hydroponics. Their agricultural systems 
always used soil.

Today hydroponics is more of a hobby than a commercial crop production method 
because of its high costs and greater technical requirements than soil 
production. There are few commercial producers of hydroponic crops. EPCOT 
Center at Walt Disney World Florida has a world famous hydroponics exhibit, 
The Land, as a popular attraction. NASA is planning on some kind of hydroponic 
system to grow plants in the space station to recycle wastes and carbon 
dioxide to produce oxygen and food.

More details can be found in my article about hydroponics history cited below.

See the references below for directions on making a simple hydroponic system 
for school use. Also use the Mad Scientist website search engine to locate 
more answers on hydroponics questions.

References


Re: What are the vitamins and minerals a plant needs for photosynthesis?


Essential Elements for Plants

Bacon, F. 1627. Sylva Sylvarum. London: J. Haviland.

Hershey, D. R. 1994. Hydroponics for teaching: history and inexpensive 
equipment. American Biology Teacher 56:111-118. 

Hoagland, D.R. and Arnon, D.I. 1950. The water-culture method for growing 
plants without soil. Circ. 347. Univ. of Calif. Agric. Exp. Station, Berkley.

Woodward, J. 1699. Some thoughts and experiments concerning vegetation. 
Philosophical Transactions of the Royal Society, 21,193-227.


Re: How to do a hydroponics project?


Re: How can I conduct a hydroponic experiment?


Re: Which plants are best suited for hydroponics and why?


Re: Does plant food like miracle-gro work better on plants than just water?


Re: How do I build a small hydroponic system in a fish tank?


Essential Elements for Plant Growth: Hydroponics