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.

Types of Fertilizers

1. Inorganic fertilizers

• Industrially manufactured chemicals.
• Contains more nutrients than organic manure.
• Nutrients are destroyed by leaching, runoff, evaporation, soil stabilization or consumption of weeds, etc.

2. Organic manure

• These are plant and animal wastes that are used as nutrients after decomposition.
• Improves tillage, aeration, water holding capacity, and micro-organism activity of the soil.

Where to apply manures?

• In fully grown trees, the manures and fertilizers should be given over the area, where their active roots are spread.
• Fertilizer should be given in restricted areas i.e., in the surrounding area of about 1 to 1.5 m away from the trunk of the trees.

Fertilizer application time

• It should be applied when the plants need it.
• Timing depends on the type of fertilizer and climate.
• Fruit trees require more nutrients at the time of new flowering and flower bud differentiation.
• Used more during fruit development.
• Nutrients should be available to them in February-March.
• Therefore, it would be better to use them in October-November for the trees to be available from February to March.

Nutrient Contents of Organic Manures

Nutrient Contents of Organic Manures 

Methods of Fertilizer Application

A) Broadcasting

• It implies spreading the fertilizers evenly throughout the field.
• 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 leafy vegetables, intended to supply nitrogen in a readily available form to growing plants.

Disadvantages of broadcasting

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

B) Band placement

• It refers to the application of fertilizer to the band/strip. It is prevalent in the application of fertilizers to the orchard. In this method, the fertilizers are kept close in the band on one or both sides of the plant. The length and depth of the band vary with the nature of the crop. Fertilizers in solid and liquid forms can be applied. The quantity of fertilizer may have economized.

C) Ring Placement

• Fertilizers are usually given to fruit trees by this method.
• Fertilizers are given in a ring, which encircles the trunk of the tree and extends to the entire canopy.
• It is more laborious and expensive.

Advantages of placement of fertilizers

1. When fertilizer is placed, there is minimal contact between soil and fertilizer, and thus nutrient fixation is greatly reduced.
2. Weeds cannot use fertilizers in the field.
3. The residual response of fertilizers is usually high.
4. Fertilizers are more used by plants.
5. Nitrogen loss is reduced by leaching.
6. Being immobile, phosphate is better utilized when placed

D) Foliar application

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

E) Starter solutions

Starter solutions specifically refer to the application of a solution of N, P₂O_5, 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 starter solution is prepared either by dissolving a concentrated fertilizer mixture at a concentration not exceeding 1%.

The disadvantages of starter solutions are 

(i) Requires additional labor, and

(ii) Fixation of phosphate is high.

F) Application through irrigation water (Fertigation)

• Application of fertilizers in irrigation water in either open or closed systems.
• Nitrogen and sulphur are the principal nutrients applied.
• Phosphorous fertigation is less common because of formation of precipitates takes place with high Ca and Mg containing water.

Advantages

• Nutrients especially nitrogen can be applied in several split doses at the time of greatest need of the plant.
• The nutrient is mixed with water and applied directly near the root zone, as such higher use efficiency.
• Cost of labour is saved.

G ) Tree Injection

• Direct injection of essential nutrients into the trunk of the tree.
• Iron salts are injected into chlorotic trees, which are deficient in iron.