WHAT ARE FERTILIZERS?
Fertilizers are any organic or inorganic material of natural or synthetic origin (other than liming materials) that are added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40% to 60% of crop yields are attributable to commercial fertilizer use. PLANT NUTRIENTS
All plants require nutrients to survive and grow. Plants take nutrients from the air, the soil, and the water. Nutrients are colourless gases or are like dust dissolved in water or stuck onto each piece of soil. The quantity of nutrients available to the plants is affected by: • substrate quality
• water quality
• plant type.
Nutrients are taken up by the fine root hairs, not by the big roots. Even the very largest of trees have many small, fine root hairs to absorb the nutrients and water they need. The larger roots are used for supporting the tree and for storage of water and other plant food. The root hairs can also excrete liquids that affect the acidity of the soil (pH). When the pH changes, the amount of nutrients available may also change. There are two sorts of nutrients: macronutrients, required in large quantities, and micronutrients, required in small quantities. The big three, nitrogen, phosphorus and potassium, together comprise over 75% of the mineral nutrients found in the plant. Macronutrients
There are 16 nutrient elements required to grow crops. Three essential nutrients—carbon (C), hydrogen (H), and oxygen (O2)—are taken up from atmospheric carbon dioxide and water. The other 13 nutrients are taken up from the soil and are usually grouped as macronutrients (primary nutrients and secondary nutrients) and micronutrients. The primary nutrients—nitrogen (N), phosphorus (P), and potassium (K)—are commonly found in blended fertilizers such as 10-10-10, or equivalent grades. Primary nutrients are utilized in the largest amounts by crops, and therefore, are applied at higher rates than secondary nutrients and micronutrients. The secondary nutrients—calcium (Ca), magnesium (Mg), and sulfur (S)—are required in smaller amounts than the primary nutrients. The major source for supplementing the soil with calcium and magnesium is dolomitic lime (aglime), although these nutrients are also available from a variety of fertilizer sources. Sulfur is available in fertilizers such as potassium and magnesium sulfate, gypsum (calcium sulfate), and elemental sulfur. Micronutrients—iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), and molybdenum (Mo)—are required in even smaller amounts than secondary nutrients. They are available in manganese, zinc and copper sulfates, oxides, oxy-sulfates and chelates, as well as in boric acid and ammonium molybdate. Primary Nutrients and Plant Growth
Of the three major nutrients, plants require nitrogen in the largest amounts. Nitrogen promotes rapid growth, increases leaf size and quality, hastens crop maturity, and promotes fruit and seed development. Because nitrogen is a constituent of amino acids, which are required to synthesize proteins and other related compounds, it plays a role in almost all plant metabolic processes. Nitrogen is an integral part of chlorophyll manufacture through photosynthesis. Photosynthesis is the process through which plants utilize light energy to convert atmospheric carbon dioxide into carbohydrates. Carbohydrates (sugars) provide energy required for growth and development. The chemical equation for photosynthesis is 6CO2 + 12H2O + 672 Kcal radiant energy = C6H12O6 + 6H2O + 6O2 Of all the elements required for crop production, nitrogen poses the greatest environmental threat through contamination of surface and ground water. Nitrogen...
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