Part 4 (1) Plant Nutrition

The nutrients needed by most agricultural plants are broken down as follows;

Macronutrients:

• N = Nitrogen
• P = Phosphorus
• K = Potassium
• Ca = Calcium
• Mg = Magnesium
• S = Sulfur
• Si = Silicon

Micronutrients (trace levels) include:

• Cl = Chlorine
• Fe = Iron
• B = Boron
• Mn = Manganese
• Na = Sodium
• Zn = Zinc
• Cu = Copper
• Ni= Nickel
• Mo = Molybdenum

If we start at the top, Nitrogen (N) we can give a brief description of how this is made available to plants;

The Nitrogen Cycle:

The earth's atmosphere is about 78 to 80% Nitrogen, and Nitrogen is essential to every living thing on earth. In plants N is used in chlorophyll molecules which are essential for photosynthesis which occurs in plants, algae and many species of bacteria, and converts carbon dioxide into organic matter, especially sugars. For our purposes and without going into too much detail, the Nitrogen cycle is as follows;

While N is abundant in the atmosphere, most of it cannot be used by plants, so gaseous N has to be processed into forms that can be used by living organisms and this is what the N cycle does. Some N fixation is done by lightening strikes, but most is done by free living bacteria that have symbiotic relationships with other living organisms. An example of this are the Rhizobium bacteria which live in the root nodules of certain leguminous plants such as beans or peas. Here they live in symbiosis with the plant, producing ammonia from atmospheric N which they then convert to carbohydrates which are used by plants. So this is a part of the N cycle where N2 is converted into a form that is readily available to plants and hence to animals. This type of conversion is known a 'Biological Fixation' and is one of four ways that N can be made available to plants and animals. The other three ways are;

• Industrial fixation, which are man made fertilizers which, because of their concentrated nature, poison the environment.
• Combustion of fossil fuels, engines and thermal power plants which produce various nitric oxides and these also poison the environment.
• Natural phenomenon such as lightening, veld fires, decomposition of dead plant or animal life etc.

Nitrates are then converted back to N2 by dentrifying bacteria in anaerobic conditions and the process (N cycle) begins again.

This is a very basic description of some of the roles played out in the N cycle, but as I have already stated, it is a vast subject. What I have written down, however, does spell out the necessity for farmers to revert to Organic Agriculture. The big problem with 'modern' agricultural methods, is that the chemical fertilizers, pesticides, fungicides and herbicides have long term negative impact upon the soils, rivers, lakes, the air we breathe etc, etc. Fortunately, Mother Nature is a powerful force, and will re-establish her natural balance, given the chance, very quickly.

More to come, keep watching........