About fertilisers (Part I)
About fertilisers (Part I)By Judith Lungu
Thursday April 03, 2008 [04:00]
Since the beginning of agriculture, it was observed that the first crop yield on a new field was higher than those of subsequent years. As a result, farmers moved from one area to another in order to get high yields.
Plants take up nutrients from the soil for their growth and yield. The supply of these nutrients in soil is limited. As plants are harvested, the nutrients are depleted from the soil resulting in reduced quality and yield of subsequent crops.
Fertilisers are natural or artificial substances added to the soil or applied directly to crop foliage to improve plant growth and yield. The addition of fertiliser to soils is necessary to correct natural deficiencies in the soil, and to replace the chemical components absorbed by the crops during growth and removed by harvesting, grazing, leaching or erosion.
The use of natural or artificial substances containing chemical elements to improve plant growth is old. Ancient Greek and Roman writings reported use of manure and composts. Substances such as animal manure, ashes from burned weeds, vegetable wastes, wastes from manufacturing processes and assorted trash were used.
Organised fertiliser technology research began in the seventeenth century. In 1840 a scientist Justus von Liebig published his research findings in which demonstrated that adding nitrogen, phosphorus and potassium to soil stimulated plant growth. By 1849, mixed chemical fertilisers were sold commercially in the United States but their use became widespread after 1900.
Fertiliser technology became more and more refined as chemical needs of growing plants were discovered. In addition new substances that improved plant growth were also being discovered. Fertiliser can now be made to suit the type of crop that is grown and can be applied in solid, liquid, or gaseous form.
There are 13 nutrient elements essential for plant growth and yield. Out of these are three primary nutrients - nitrogen, phosphorus and potassium which are required in large amounts by the plant.
These are the elements which almost always limit plant growth if inadequate. Sulfur, calcium and magnesium are termed secondary nutrients because although they are necessary for plant health and growth, they are required in lesser amounts. The trace elements boron, chlorine, cobalt, copper, iron, manganese, molybdenum and zinc are required by plants in very small amounts and are the least likely to be limiting plant growth in many soils. A fertiliser contains one or more of these nutrient elements.
The three primary elements nitrogen, phosphorus and potassium have major effects on plant growth and yield. Nitrogen promotes rapid plant growth, formation of chlorophyll and protein synthesis. If nitrogen is deficient in the soil, plants will not grow vigorously and the leaves will become yellow because of reduced chlorophyll formation.
Phosphorus stimulates early root growth, hastens maturity, and stimulates blooming and seed formation. If phosphorus is deficient, the plant will have short slender stalks, fruiting will be delayed and there will be less vegetative growth.
Potassium increases resistance to drought and disease, increases stalk and straw strength and increases grain and seed quality. Deficiency of potassium leads to large and small spots of dead tissue; older leaves are scotched and die at their tips and outer margins. Cobs of maize will not be filled to the end.
Fertilisers are divided into two groups; organic and chemical (inorganic or mineral) fertilisers. Organic fertilisers are from animal and plant origin. Chemical fertilisers are manufactured and may be formulated in appropriate concentrations and combinations for various crops and growing conditions.
The most commonly used chemical fertilisers are compound fertilisers consisting of the primary elements nitrogen, phosphorus and potassium.
The containers of fertiliser are labeled with three numbers representing nitrogen, phosphorus and potassium or N-P-K code. The numbers represent quantity of these primary elements. For example a 50kg bag of fertiliser which is labeled 6-12-12 contains 6 per cent by weight nitrogen, 12 per cent by weight phosphorus and 12 per cent by weight potassium.
This type of fertiliser is called a complete fertiliser because it has all the three primary elements.
Secondary nutrients may be blended in a compound fertiliser. This will be indicated on the back of the bag. It will also be expressed as a per centage of total material for example a 50 kg compound fertiliser of (N-P-K) 6-12-12 containing 15 percent sulphur will be labeled 6-12-12+15 S.
An incomplete fertiliser will be missing one or more of the primary elements eg Urea containing 46-0-0 has 46 per cent by weight nitrogen only. This is incomplete fertiliser. Triple super phosphate with 0-46-0 has 46 per cent by weight phosphate without nitrogen or potassium.
This is also incomplete fertiliser. Incomplete fertilisers can be blended to make complete fertiliser. However it is easier to use a complete fertiliser because it is already blended.
The best fertiliser to use depends on the needs of the soil. The needs of the soil are determined by soil tests. If the soil has high levels of phosphorus and potassium, then a 46-0-0 that is a fertiliser with nitrogen only, this may be the appropriate choice of a fertiliser to use at or near planting time. (Part II, types of fertiliser and fertiliser applications).
Labels: AGRICULTURE, FERTILIZER
posted by MrK @ 6:22 AM
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Fertilisers (part II)
By Judith Lungu
Thursday April 17, 2008 [04:00]
There are 16 nutrient elements that are essential for the growth of plants.
The most abundant are carbon, hydrogen and oxygen which plants get from air and water. It is the other 13 that are of concern which plants get from the soil. If they are not adequate they should be applied in form of fertiliser.
The 13 nutrients are divided into 3 groups. These are primary elements consisting of nitrogen (N), phosphorus (P) and potassium (K) which are needed in large quantities, the second are secondary elements like calcium (Ca), magnesium (Mg) and sulfur (S) which are needed in less quantities by plants and the third are micronutrients zinc (Zn), manganese (Mn), iron (Fe), boron (B), copper (Cu), molybdenum (Mo) and chlorine which the plants need in very small quantities but are still essential. A fertiliser is called complete if it contains each of the major elements-nitrogen, phosphorus and potassium. Fertilisers are grouped into two groups - organic or inorganic fertilizers.
Organic fertilisers are derived from plant or animal sources. They have small amounts of nutrients but these are released slowly over an extended period of time.
This is because soil micro-organisms must first break down plant and animal material to free the nutrients. These nutrients can then be taken up from the soil by the growing plant. Because of the slow release of nutrients, organic fertilisers need not be applied very often.
Examples of organic fertilisers include animal manures, compost, sludge, industrial byproducts and many others. Animal manures are a complete fertiliser because they contain all the major elements (NPK) although in small amounts. The highest nutrients are found in fresh manure. The nutrient content of animal manures decrease as the material ages or is composted. However aged or composted material is the one used in the field in order to prevent the burning of plants and it is easier to spread. Chicken manure will burn plants if applied when fresh.
Organic fertilisers do more than add nutrients. They improve soil by increasing organic matter, improving soil physical properties and increasing microbial activity of the soil.
Inorganic fertilisers are manufactured artificially. The nutrients added in the fertiliser can be varied according to needs of the plants.
The nutrients are readily available to the plant when applied to the soil. They are also easily depleted because the nutrients are used quickly. The plant responds to the application of artificial fertiliser very quickly but that means inorganic fertiliser must be applied often or timed for a specific period during growth of the plants.
All inorganic fertilisers are labeled with NPK numbers. The ratio describes the relative proportions of nitrogen, phosphorus and potassium. For example D-Compound is labeled 10-20-10 indicating 10 parts nitrogen, 20 parts phosphorus and 10 parts potassium while X-Compound is 20-10-5. A fertiliser is said to be balanced if it has equal parts of NPK such as 10-10-10.
There are special fertilisers packaged for certain types of plants. Fertilizer dealers have computer programmes that can quickly determine the most cost effective fertiliser blend and most needed nutrients for your field based upon a soil test report. Laboratories for soil tests are at University of Zambia, Soil Science Department, Zambia Agriculture Research Institute (ZARI) both in Lusaka. However, fertiliser Suppliers are increasingly developing their laboratories and staff capacities so that they can provide the fertiliser products needed by farmers.
The ratio of nutrients required depends on nutrient requirements of the crop and the levels of available nutrients in the soil where the crop is planted. As already stated, you need soil test to determine the needs of your soil. Where GIS is used, the right amounts of fertiliser is applied in all areas.
Different crops have different nutrient requirements. Root crops require less nitrogen fertilisation than leafy crops. Maize is a heavy nitrogen feeder that is why urea or ammonium nitrate are given to the crop as top dressing. Most trees and shrubs perform well with one application per year.
Fertilisers come in various forms, sizes and combinations. The type or form is called a formulation. Formulations come as water soluble powders, slow release pellets or spikes, liquids, tablets and granular solids. Application of fertilizer is also varied.
Fertiliser is applied by broadcasting, banding, side dressing, fertigation or foliar feeding. Broadcasting entails spreading fertiliser over a growing area and incorporating it in the soil. Banding is putting fertiliser in furrows on the side and below the seeds or plants to be planted. Side dressing is putting fertiliser on the sides of plants when the plants are already growing. Foliar feeding is using soluble fertiliser diluted in water and spraying it on plants.
I would like to take a few issues.
1) Organic fertilizer is not necessarily slow acting at all.
Worm castings are immediately available, and do not burn the plant. In fact, worm manure is a very natural form of manure that is naturally available.
2) Animal manures like chicken, cattle, pig manure need time to be broken down by bacteria, or they create heat which damages the plant's roots.
3) Is the chemical fertilizer industry pushing the idea that organic fertilizer is inferior to chemical fertilizer?
Two alternatives to chemical fertilizer are worm castings, which can be made on the farm, and compost, which adds both nutrients and organic matter to the soil.
Because organic ferts actually improve the soil, and don't deplete it or kill bacteria.
Vermico - Why is the worm industry expanding?
Earthwormdigest - The #1 earthworm Information Website In The World
Global Worm Tea
My Green Corner - Worm Tea
Wiser Worm Farm - Worm Tea
Compost Guide
TRASH TALKING WITH WORMS
The Dirty Truth About Worm Composting
By Eric Vinje, Planet Natural
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