Methods 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:

1. Kind of soil we are ploughing
2. Type of crop we are taking
3. Nature of nutrient we are applying
4. 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.

These are several methods of applying manures and fertilizers in vegetable crops. These are discussed below one by one:

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.

Which fertilizer should be applied and how?

• Since 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.
• Likewise, a 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.

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 tomato, 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:
  
  1. Small quantity of micronutrient is needed to apply.
  2. It cannot be applied effectively through root or soil,
  3. 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

Table2: Recommendations for foliar applications of plant nutrients.

Source: Donald N. Maynard and George J. Hochmuth, Knott's Handbook for Vegetable Growers, 4th edition (1997).

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.

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.

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 sulphur 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.