In order to get the maximum benefit from manures and fertilizers, they should not only be applied at the proper time and in the right manner but other aspects should also be carefully considered. Different fertilizers react differently with the soil. Similarly, different crops have different N, P, K requirements and even the nutrient requirements for the same crop are not the same at different stages of growth. The aspects which need to be considered in the application of fertilizer are listed below:

• Availability of nutrients in manures and fertilizers.
• Nutrient requirements of crops at different stages of crop growth.
• Time to application.
• Methods of application, selection of fertilizers.
• Crop response to fertilizer application and the interaction of N, P, and K.
• The residual effect of manures and fertilizers.
• Crop response to various nutrient carriers.
• The unit cost of nutrients.

Fertilizer application timing and method may vary –

1) Nature of fertilizer.

2) soil type and

3) Difference in nutrient requirement and nature of field crops.

Methods of Fertilizer Application

The different methods of fertilizers application are as follows:

A) Broadcasting

1. It implies spreading the fertilizers evenly throughout the field.
2. Suitable for dense crops, the roots of the plants, covering the entire soil, application of high amounts of fertilizers, and insoluble phosphatic fertilizers such as rock phosphate.

Fertilizers are broadcast in two ways.

 i) Broadcasting at sowing or planting (Basal application)

Broadcasting of fertilizers at the time of sowing means distributing the fertilizers evenly throughout the field and mixing them into the soil.

ii) Top dressing

It is the broadcasting of nitrogenous fertilizers specifically to intensively sown crops such as paddy and wheat, intended to supply nitrogen in a readily available form to growing plants.

Disadvantages of broadcasting

1. Nutrients cannot be fully utilized by the roots of the plants as they are scattered at a distance from the roots.
2. Increase in weeds throughout the field.
3. Nutrients become fixed in the soil as they come into contact with a larger mass of soil.

B) Placement

1. It refers to the placement of fertilizers in the soil at a specific location with or without the known position of the seed.
2. The application of fertilizers is generally recommended when the amount of fertilizers is low, root system development is poor, soil fertility levels are low and phosphatic and potassium fertilizers are to be applied.

The most common methods of placement are as follows:

i) Plough sole placement

1. In this method the fertilizer is applied in a continuous band/strip at the bottom of the plow furrow during the tillage process.
2. When the plow is turned in the next round, each band is covered.
3. This method is suitable for areas where the soil surface becomes quite dry to a few centimeters below and the soil has a heavy clay pan just below the plow layer.

ii) Deep placement

It is particularly used in the application of ammoniacal nitrogen fertilizers to soil reduction zones in paddy fields, where ammoniated nitrogen is available for the crop. This method ensures better distribution of fertilizer in the soil of the root zone and prevents loss of nutrients by runoff.

iii) Localized placement

It refers to the application of fertilizers to the soil near the seed or plant in order to supply sufficient amount of nutrients to the roots of growing plants. Common methods of applying fertilizers to the seed or plant are as follows:

a) Drilling

In this method, fertilizer is applied at the time of sowing through seed-cum-fertilizer drill. It places fertilizer and seed in the same row but at different depths. Although this method has been found suitable for the application of phosphatidic and potash fertilizers in cereal crops, sometimes the germination of seeds and young plants can be damaged due to the high concentration of soluble salts.

b) Side dressing

This refers to the spread of fertilizer between rows and around the plants. Common methods of side-dressing are

1. manual placing nitrogenous fertilizers between rows of crops like maize, sugarcane, cotton etc. to provide additional doses of nitrogen for growing crops and
2. manual application of fertilizers around trees like Mango, Apple, Grapes, Papaya etc.

C) Band placement

It refers to the application of fertilizer to the band/strip. There are two types of band placement.

i) Hill placement

It is prevalent in the application of fertilizers to the orchard. In this method the fertilizers are kept close in band on one or both sides of the plant. The length and depth of the band varies with the nature of the crop.

ii) Row placement

When crops like sugarcane, potato, maize, cereals etc. are sown in rows, the fertilizer is given in a continuous band/strip on one or both sides of the row, which is known as row placement.

D) Pellet application

1. It refers to the application of nitrogenous fertilizers in the form of pellets 2.5 to 5 cm deep between the rows of paddy crop.
2. Small balls/pellets of convenient size are made by mixing the fertilizers with soil in the ratio of 1:10 for application to the soil of paddy fields.

e.g.:- Row Placement

Advantages of placement of fertilizers

The main advantages are as follows:

i) When fertilizer is placed, there is minimal contact between soil and fertilizer, and thus nutrient fixation is greatly reduced.

ii) Weeds cannot use fertilizers in the field.

iii) Residual response of fertilizers is usually high.

iv) Fertilizers are more used by plants.

v) Nitrogen loss is reduced by leaching.

vi) Being immobile, phosphate is better utilized when placed

 Following are the common methods of applying liquid fertilizers

A) Starter solutions

t specifically refers to the application of a solution of N, P₂O₅ and K₂O in the ratio 1:2:1 and 1:1:2 to young plants at the time of transplanting vegetable seedlings. Starter solution helps in the faster establishment and faster growth of seedlings. 

The disadvantages of starter solutions are 

(i) Requires additional labor, and

(ii) Fixation of phosphate is high.

B) Foliar application

1. It refers to the spraying of a fertilizer solution containing one or more nutrients on the foliage of growing plants.
2. Many nutrients are easily absorbed by the leaves when they are dissolved in water and sprayed on them.
3. The concentration of the spray solution has to be controlled; Otherwise, scorching of leaves can cause serious damage.
4. Foliar spraying is effective in delivering minor nutrients such as iron, copper, boron, zinc, and manganese. Sometimes pesticides are used along with fertilizers.

C) Application through irrigation water (Fertigation)

1. It refers to the delivery of water-soluble fertilizers through irrigation water.
2. The nutrients are thus carried into the soil in solution.
3. Generally, nitrogenous fertilizers are applied through irrigation water.

D) Injection into the soil

1. Liquid fertilizers for injection into the soil are given in two ways, either under pressure or without pressure.
2. Non-pressure solutions may be applied either on the surface or in furrows without appreciable loss of plant nutrients under most conditions.
3. Anhydrous ammonia should be placed in narrow grooves at a depth of 12-15 cm and immediately covered to prevent loss of ammonia.

E) Aerial application

In areas where it is not practical to fertilize on the ground, the fertilizer solution is given by plane especially in hilly areas, in forest land, in grasslands or in sugarcane fields etc.