Fertilizer
Fertilizers are substances that can be organic or inorganic that is added to the soil to improve its growing capacity and supply essential nutrients to the plant.
Ancient farmers knew that the first yields on a plot of land were much better than those of subsequent years. This caused them to move to new, uncultivated areas, which again showed the same pattern of reduced yields over time. Eventually it was discovered that plant growth on a plot of land could be improved by spreading animal manure throughout the soil.
Over time, fertilizer technology became more refined. New substances that improved the growth of plants were discovered. The Egyptians are known to have added ashes from burned weeds to soil. Ancient Greek and Roman writings indicate that various animal excrements were used, depending on the type of soil or plant grown. It was also known by this time that growing leguminous plants on plots prior to growing wheat was beneficial. Other types of materials added include sea-shells, clay, vegetable waste, waste from different manufacturing processes, and other assorted trash.
Organized research into fertilizer technology began in the early seventeenth century. Early scientists such as Francis Bacon and Johann Glauber describe the beneficial effects of the addition of saltpeter to soil. Glauber developed the first complete mineral fertilizer, which was a mixture of saltpeter, lime, phosphoric acid, nitrogen, and potash. As scientific chemical theories developed, the chemical needs of plants were discovered, which led to improved fertilizer compositions. Organic chemist Justus von Liebig demonstrated that plants need mineral elements such as nitrogen and phosphorous in order to grow. The chemical fertilizer industry could be said to have its beginnings with a patent issued to Sir John Lawes, which outlined a method for producing a form of phosphates that was an effective fertilizer. The synthetic fertilizer industry experienced significant growth after the First World War, when facilities that had produced ammonia and synthetic nitrates for explosives were converted to the production of nitrogen-based fertilizers.
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[edit] Types of Fertilizers
Fertilizers are broadly classified into Organic and Inorganic(chemical) fertilizers.
[edit] Organic fertilizers
- Main Article: Organic fertilizer
Organic fertilizers are the most convenient forms of fertilizers. They are safe and easily available. Things like manure, slurry, worm castings, peat moss, seaweed, sewage and guano are good examples of organic fertilizers. Vegetation material called mulch, such as hay, peat moss, leaves, grass, bark, wood chips, seed hulls, and corn husks all help to aerate the soil, insulate the ground against temperature change, and add needed nutrients.
Apart from these naturally occurring minerals like sulfate of potash, limestone and rock phosphate are also considered very good organic fertilizers.
Advantages of Organic Fertilizers
- Improve the structure of the soil.
- Retain soil moisture.
- Release nitrogen slowly and consistently.
- Mobilize existing soil nutrients.
- Do not burn the plants like some chemical fertilizers
- Less subject to leaching
Disadvantages of Organic Fertilizers
- Often Organic fertilizers, especially those that contain animal and plant feces are contaminated with pathogens. Make sure they are properly composted to reduce the risk of pathogens.
- The composition of organic fertilizers is variable thus it becomes a very dilute and inaccurate source of nutrients compared to Inorganic type of fertilizers. For profitable yields, significantly large amounts of fertilizers should be used to cope up with nutrient requirements.
[edit] Inorganic fertilizers
Inorganic fertilizers are primarily derived from chemical compounds such as ammonium nitrate, ammonium phosphates and potassium chloride. Chilean sodium nitrate, mined rock phosphate and limestone are examples of inorganic Fertilizers.
Advantages of Inorganic Fertilizers
- Higher and accurate amount of nitrogen promotes protein and chlorophyll and encourages growth of stems and leaves.
- Higher amount of phosphorus results more flowers, larger fruits, and healthier roots and tubers.
- Potassium from potash fosters protein development and thickens stems and leaves.
- Release of nitrogen rapid.
- Accurate source of nutrients.
Disadvantages of Inorganic Fertilizers
- When used carelessly it can burnplants and distort the quality of soil leading to cadmium poisoning.
- Using inorganic fertilizers would mean that strict watering schedules have to be adopted in order to retain the soil moisture.
- Inorganic fertilizers are made up of elements like potassium and phosphorus that come from mines or saline lakes thus from limited resources.
[edit] Method of fertilizer application
It is very important to choose the right method of fertilizer application. Choice of method of fertilizer and its application mainly depends on:
- Kind of soil we are ploughing
- Type of crop we are taking
- Nature of nutrient we are applying
- Irrigation facility in the area i.e. the land is irrigated or rain fed.
- Nutrients to be used by plant must be placed in such a manner that they can be dissolved by the moisture in the soil. The rates and distance that plant food element can move within the soil depend on the chemical nature of the material that furnishes the nutrients and character of soil.
[edit] Soil application
Organic manures are mostly spread uniformly in the field and incorporated several days before planting. Following are most important methods of application of fertilizers.
- Broadcasting on the soil surface before ploughing.
- Broadcasting on the soil surface after ploughing and mixing with the surface soil by harrowing.
- Applying fertilizers in a band at the bottom of the plough furrow.
- Applying fertilizers in bands, 5 to 8 or more centimeters from the row and 5 to 8 or more centimeters below the surface.
- A combination of broadcasting methods or plough furrow application with bands at the side of the row to planting time.
- Applying fertilizer with a drill below the surface of the soil before crop is planted.
[edit] Type of fertilizers
- Phosphates generally move only short distance from their points of placement so for better availability, phosphates must be placed in the zone of root development for being utilized by plant. Surface application after a crop is planted not being in the zone of root activity, is of little value to row crops in the year of application.
- The placement of water soluble phosphorus in bends tends to reduce contact with the soil and result in lesser fixation than in broadcast application.
- In contrast to phosphorus, the nitrates salts are mobile and move vertically or horizontally within the soil as the water moves. In fine textured soil the movement of N is restricted.
- Potassium salts are less mobile than the nitrates but are more mobile than P.
- In general, N and K carrying fertilizers are more readily soluble than the P material. Therefore, they cannot be safely concentrated in as large amount near the seed or the roots of plants because of the danger of salt damage.
- Reduction of soil moisture increases the concentration of the soil solution. Therefore, relatively large amount of fertilizers placed too near the seed or seedling roots are likely to cause injury during the dry periods, practically when such periods occur soon after the application of fertilizer.
- It is desirable to divide the total requirement of fertilizer nitrogen into several parts to be applied from time to time during growing season. Fertilizers rich in' potassium should be placed in a band to the side and below the seed or transplant.
[edit] Starter Solution
Solution of fertilizers consisting of N, P, and K is prepared in desirable concentration and directly applied to the roots of young plants at the transplanting time. Such solution is termed as "Starter solution". This method allows a direct utilization of cheapest Nitrogen and phosphorus sources.
Advantages
- The nutrients reach the plant roots immediately, and
- The solution is sufficiently diluted so that it does not inhibit growth.
- Starter solution stimulates growth of young plants.
- Starter fertilizer can be used in Tomatoes, peppers, melons, Cabbage, Cauliflower, and Broccoli.
Foliar spray
- Nutrients are applied in the form of dilute solution on standing crop over the leaves of the plants.
- Since there is the direct application of nutrient to the site of metabolism the nutrient use efficiency is increased and quick response is observed by plants.
- This method is more fruitful (convenient, economic and quick responsive) when:
- Small quantity of micronutrient is needed to apply.
- It cannot be applied effectively through root or Soil,
- There is need to apply partial quantity of nitrogen in the form of urea.
- It is not possible to give the total requirement of major nutrients through foliar feeding because higher concentration causes leaf scorching, and if frequency of sprays is increased, it increase cost of cultivation.
- The minimum safe concentration and frequency of spray solution's depends upon the crop, the stage of maturity, season of spraying and the wetting and adhering quality of the spray. In general, 1 to 3 sprays of micronutrients and 3 to 6 of macro element nutrition with wetting the leaves thoroughly in each spray, are advised. Table2 gives the recommended dose for
Points to keep in mind to increase absorption of nutrients applied through foliar spray:
- Mix spreaders like Triton X 100 wetting agents like Teepol, Sandovit, Tween 80, Tween 20, Glycerin and softeners like Magnesium sulphate, for Urea spray and lime for Zinc sulphate spray, increases absorption.
- Spray should be done preferably during morning after 9 A.M. and afternoon between 3 to 4 P.M. But avoid spraying in early morning hours where leaves are found wetted with dew and frost during the night. Spraying should also be avoided after 4 P.M. because by that time stomata of leaves start closing.
- Go for optimum concentration for maximum absorption of nutrients.
Spray equipments also affect absorption of nutrients. There will be more absorption of nutrients when they are applied in the form of micro fine droplets so that there is complete wetting of leaves
- There will be maximum absorption of nutrients when they are applied on plants having maximum number of functioning leaves (photosynthetically active leaves).
- Maintain 'pH of the solution round about 7.
- Kind of compound from which a particular element is absorbed efficiently by the leaves. For example Phosphorus absorption is rapid from hypophosphate.
[edit] Fertigation
In this method, fertilizers are applied to the standing crops with irrigation water. It is safe when fertilizers are applied with drip irrigation. Application through sprinkler may cause burning of foliage. Fertigation is useful method to supplement soil application.
Time of application
- Organic manures like farmyard manure, compost, leaf mould etc are incorporated in the soil well in advance to sowing/planting of vegetable crops. Doing so, these manures get mixed properly in the soil and start rotting, and nutrients are released when crop plants are in need of them.
- Chemical fertilizers are applied as a basal dose and in the form of top dressing. The basal is applied just one day before sowing or planting and mixed or drilled in the soil. Care is taken for the presence of sufficient soil moisture. Top dressing of fertilizer, particularly nitrogenous fertilizers is done 15 to 21 days after sowing/planting. This is time when mostly plants get established.
- The time of application of foliar feeding of Nitrogen and micronutrients is when plants start sowing deficiency symptoms.
[edit] Precautions in fertilizer use
- Go for soil testing. The amount of fertilizer(s) should be calculated based on soil test for balanced use of nutrients.
- Secondary nutrients like Sulfur should be used either alone or through sulphur bearing fertilizers. In acid soils, Calcium and Magnesium should be maintained at the optimum level.
- Micronutrient should be applied wherever necessary. In acidic soils boron and molybdenum, and in alkaline soils, Iron, Zinc and Manganese should be made available. Phosphate rich calcareous soils may show zinc deficiency problems.
- Fertilizers should be selected on the basis of soil characteristic that is avoid acid fertilizers in acid soils and basic fertilizers in alkaline soils.
- Improve soil structure through the addition of organic manure and gypsum. Black and alluvial soils should be deep ploughed.
- Use of high yielding varieties, irrigation at an appropriate time and amounts, removal of weeds, spacing and plant Population etc. should be taken care of.
- When above mentioned precautions are taken cares off the continuous application of fertilizers will not reduce soil fertility rather it will help in sustaining higher crop yields.
[edit] Negative of impact of fertilizer
Fertilization is considered as one of the main sources of pollution of water bodies caused by agriculture. When high fertilizer rates are applied which are not in line with the codes of good agricultural practice, nutrient losses, e.g. by surface runoff, take place which pollute land-based and aquatic ecosystems. An oversupply with inorganic nitrogen and phosphorus compounds causes an increased nitrification, oxygen demand, intensification of the primary production of plankton including "red tides", excessive growths of macro-algae and other water plants as well as formation of the toxic un-ionized ammonia.
The negative impact of nutrient losses from agriculture on ecosystems in ponds, lakes, rivers as well as to seas and oceans varies . Oxygen deficiencies in the bottom waters of shallow areas may result in the production of hydrosulfide which is highly toxic. Low oxygen concentration in deep water layers where fish spawn may prevent the development of eggs. Increased density of macro-algae in shallow waters of seas might affect the composition of species too.
