Plants require nutrients to grow and develop, much the same like people. We eat so our bodies can get the vital nutrients and minerals to grow healthy. This brings to mind the saying "you are what you eat" and it is the same with plants. Poor feeding and low nutrient levels will result in poor or diminished growth and low food, flowering and fruit production. As mentioned in organic matter we need to supplement the nutrient value of the garden soil by making soil amendments in the form of adding fertilizers, preferably organic fertilizer. These nutrients include Carbon, Nitrogen, Calcium, Hydrogen, Phosphorous, Magnesium, Oxygen, Potassium, Sulphur, Iron, Zinc, Chlorine, Manganese, Boron, Copper, and Molybdenum. Soil is the most important source of plant food.
These nutrients, present in both chemical and organic fertilizer comes in two major categories: macro elements and micro elements.
Macro elements refer to the main elements that are required by the plant for its basic functioning. These main elements are:
Of these macro elements Carbon, which is obtained from carbon dioxide of the air; Oxygen, which is obtained from air and water; and Hydrogen, which is obtained from water, are required by plants to build its basic cell structure. Thus it is most fortunate that these elements are the most commonly found elements and are required by all living creatures, therefore it is seldom that you need to provide additional carbon, oxygen or hydrogen. Potassium, Phosphorous and Nitrogen, on the other hand, are usually lacking and supplements of these need to be provided for the plants. These are thus the main ingredients in the most basic chemical and organic fertilizer.
The role of Nitrogen in plants cannot be emphasized enough; Nitrogen encourages development of plants, it is responsible for healthy green leaf growth which is the result of the formation of chlorophyll, which is the main unit for the production of carbohydrates, proteins and oxygen. Therefore, plants that exhibit a Nitrogen deficiency will show symptoms like stunted growth and pale green and yellow leaves. There are also claims that Nitrogen controls, the efficient utilization of phosphorous and Potassium. The plant's dependency on Nitrogen can also lead to retarded root growth and resulting in the foliage turning yellow and pale green and increasing the plant’s susceptibility to disease.
Phosphorous is responsible for cell development and the promotion of good root growth, particularly in fibrous roots, the vigor of the plant. Plants that suffer from a phosphorous deficiency will have poor root development and show symptoms like stunted growth, though it is not as easily recognizable at those symptoms of Nitrogen deficiency. Phosphorous deficiency is also manifested in the leaves that turn purplish in color when it is not the natural foliage or leaf color of that plant, mainly due to the abnormal increase in the sugar content and the formation of anthocyanin.
Potassium is responsible for chlorophyll formation which plays an important part in the strength of cells and encourages flower and fruit formation. Thus Potassium can enhance the ability of the plant to resist plant diseases, insect attacks and cold conditions as Potassium performs a vital role in the formation of starch as well the production and translocation of sugars in the plant. Plants that exhibit symptoms of Potassium deficiency will have like weak stems. Other symptoms of Potassium deficiency include older leaves that are floppy with yellow tips and brown margins.
A note of caution though; an excess of Potassium may tend to delay maturity, though, not to be the same extent as nitrogen.
There are also secondary macro nutrients such as Calcium, Magnesium and Sulfur.
Calcium is responsible for the construction of cell walls and promoting proper functioning of growing tissue. Fortunately Calcium occurs naturally in organic soil and there is usually no need for any calcium supplements to be added to organic garden soil. A Calcium deficiency in soil only coccurs in extremely acid soil. This is why most plants struggle to grow in acid soil. Usually, treating and amending the soil pH level will alleviate the Calcium deficiency.
Magnesium (Mg) also occurs naturally in organic soil which usually makes adding any magnesium supplements to garden soil rather superfluous. Magnesium deficiency symptoms are manifested as the yellowing of older leaves. Magnesium is part of chlorophyll and thus plays a role in photosynthesis.
Sulfur (S) or Flowers of Sulfur as it is known also occur naturally in organic soil. Most chemical and organic fertilizer also contains Sulfur which makes Sulfur deficiency very rare. If Sulfur deficiency does occur, it shows up in the form of stunted growth and yellow foliage, much the same as nitrogen deficiency as Sulfur forms part of plant protein and plays a role in the formation of chlorophyll.
Micro elements are also known as trace elements and sometimes people even call them the "multi vitamins" for plants. The micro elements of plants are made up of Iron (Fe), Zinc (Zn), Manganese (MN), Boron (B), Molybdenum (Mo) and Copper (Cu). A Molybdenum deficiency produces whip-tail in some vegetable crops such as cauliflower, broccoli and other Brassica species. The Molybdenum deficiency will reduce the activity of the symbiotic and non-symbiotic nitrogen-fixing micro-organisms. A Boron deficiency can manifest itself in varying forms that are dependent on the type of plants and the age of the particular plants afflicted with the deficiency, the particular type of conditions in which the plants is cultivated, etc. Each type of crop produces its characteristic growth abnormalities associated with boron deficiency: a few examples can be seen as the die-back and corking of apples, the yellowing and resetting of Lucerne crops and related grass type crops, the corking and pitting of tomatoes, even the hollow stem and bronzing of curd in brassica types, etc. It is seldom that a micro element deficiency occurs. Many plant food formulations contain these trace elements. However, if there is a deficiency it is normally manifested as discolored foliage, poor leaf maturation and poor fruiting.
To prevent all these deficiencies from ruining your garden experience and to ensure healthy growth and abundant flowering and fruiting you should make sure that your garden has all twelve of these elements available to them. By practicing organic gardening and keeping your garden soil healthy these deficiencies are addressed by means of organic soil amendments. (TIP: Ensure that your garden receives all of them through your plants' growth season, generally either the winter or the summer cycle.)