1. Organic fertilizers or Manures are soil amendments derived from fully decomposed plant remains and animal excrements and by-products or a combination of both that is guaranteed to contain one or more of the essential nutrients other than carbon (C), hydrogen (H) and oxygen (O). Organic fertilizers generally have low nutrient content, thus significantly large volume is required for application. Based on the cost of nutrient per pound, manure or organic fertilizer is generally expensive. However, organic fertilizers or manures contain a variety of essential micro-nutrients that plant need. They also help improve the physical and chemical properties of the soil by increasing soil organic matter content. Compost, animal manures, green manures, bone meals, fish meals, and blood meals are common examples of organic fertilizers.
Even human manure is also a source of organic fertilizer. Although human feces and urine as fertilizer, modernly referred to as Humanure, is just beginning to shine in this part of the globe, it has been used in China, where it is called Night Soil, for thousands of years. I have seen toilets built along the rural roads of southern China where the tank is left open for easier collection.
Green Manuring is the process by which a crop, usually a ground cover, is planted and then plowed under and allowed to decompose in order to add nutrient and organic matter in the soil. Green manure crops are grown to improve the soil and indirectly improve crop yields. Plants used as green manure are generally fast-growing, herbaceous, and fast-decomposing. I'd prefer "green-manured" salad than its "humanured" counterpart...psychology seems to mess up my scientific view of the matter.
The nutrients from organic materials have to be broken down into inorganic molecules before they can be absorbed by the plant. This process by which organic material is converted into forms useable by plants is called decomposition. Decomposed organic material is called compost. Soil bacteria action hastens decomposition and bacterial activity is a function of temperature.
2. Inorganic Fertilizers or Synthetic Fertilizers are manufactured from natural materials such as petroleum and natural gas. They contain high percentages of nutrient content. When applied properly at the right amount, they result in relatively fast plant response. On the other hand, it is also easy to apply too much fertilizer, causing damage to the plants. Nutrient from inorganic fertilizers is released readily in the soil varying slightly depending on the fertilizer. Since the nutrients are readily available, there is a higher risk of nutrient loss through run off or leaching.
Nitrogen, phosphorous and potassium commonly known as NPK are the elements required by plants in huge quantities. Because of this they are considered the primary elements. When there is a deficiency of these elements in the soil, the plants show symptoms of abnormal growth and development. Inorganic fertilizers are classified based on their NPK components: complete and incomplete fertilizer.
- Complete Fertilizer is any inorganic fertilizer containing nitrogen, phosphorous and potassium. NPK are required components of complete fertilizer. Complete fertilizer comes in different fertilizer ratio which is the relative amount of N to P to K. In other words it is the proportion by which the elements are represented in the fertilizer. The fertilizer ratio can be calculated by dividing the greater grades by the least grade. A triple sixteen (16-16-16) has 1:1:1 ratio, while 30-10-20 has 3:1:2 ratio. By varying ratio farmers or gardeners get to choose the right fertilizer depending on the requirements of the plants and the condition of the soil they work with. Fertilizers with the same ratio do not have to have the same grade.
- Examples of complete fertilizers:
- Triple twelve (12-12-12)
- Triple sixteen (16-16-16)
- Thirty ten twenty (30-10 20
- Incomplete Fertilizer is a synthetic fertilizer containing one or two of the primary elements (N), nitrogen, phosphorous (P) and potassium (K). They can either contain just one element or a combination of any two of N, P, and K. These are useful for application in areas where only one or two of these three elements are deficient. Incomplete fertilizers may be combined to form a complete fertilizer when necessary.
- Examples of incomplete fertilizers:
- Ammonium Sulfate (21-0-0)
- Ammonium Nitrate (34-0-0)
- Sodium Nitrate (16-0-0)
- Urea (45% N)
- Urea formaldehyde (38% N)
- Rock Phosphate (16% N)
- Super Phosphate (20% P)
- Triple Phosphate (46% P)
- Muriate of Potash (60% K)
Know your plants and soil, choose fertilizer correctly.