Soil Nutrients (Soil Fertility)

Under the section on “Soil Aeration” (Chapter 4), it was explained that all living plants respire. This is the process where oxygen is used to burn food into carbon dioxide and water. Now we will consider another process used by green plants to manufacture their own food called “photosynthesis,” In photosynthesis, carbon dioxide and water are used along with light energy in the plant cell chloroplasts (containing chlorophyll) to produce their own food (carbohydrates) with oxygen produced as a by-product: Although this seems to be the opposite process from respiration, yet there are differences. Note that light energy and chlorophyll are required in photosynthesis. Chlorophyll is the green coloring matter in plants. There are, at present, seventeen (17) elements that plants need to grow and complete their life cycle. These are called “essential elements” or “nutrients.” Usually an essential element cannot be completely replaced by any other element. There are also four (4) other elements, although not essential, that help plants to grow better. These are called “functional” or “metabolic.” To remember all of these elements a memory aid, a mnemonic (the first letter is silent) has been devised. The 21 elements used by plants, carbon (C), hydrogen (H), oxygen (O), phosphorus (P), potassium (K), nitrogen (N), sulfur (S), calcium (Ca), magnesium (Mg), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), molybdenum (Mo), vanadium (V), boron (B), silicon (Si), chlorine (Cl), and sodium (Na), can be listed in their chemical abbreavtions with the mnemonic below: The elements carbon, hydrogen, and oxygen can be considered nonmineral elements, as these are obtained by plants from air and water (O2, CO2, and H2O) and not from the soil. Plants use these three elements to form simple carbohydrates from which large amounts of more complex plant compounds (about 95% of plant tissue) are formed. There is little control of these elements by man, except for water. Supplemental CO2 has been provided to plants to increase photosynthesis by using solid CO2 (dry ice), hut this has not proved economical.