Principles and Methods of Fertilizer Application

After reading this article you will learn about the principles and methods of fertilizer application.

Principles of Fertilizer Application:

1. Frequency of Fertiliser Application:

Usually larger quantities of fertilisers are added to clayey soils at longer intervals, than to the sandy soils because clayey soils are richer in humus than sandy soils and both clay and humus have a high capacity to retain nutrient ions, by a phenomenon called Base Exchange.

These absorbed nutrient ions are not lost by leaching and can be gradually taken up by the roots. If a heavy dose of water soluble fertiliser is applied to a sandy soil, most of it will be leached down by high rainfall in the humid region.

2. Quantity of Fertiliser to be Applied:

Cultivated soils where grain crops are raised have been placed in Low, or Medium or High categories, according to their content of available Nitrogen and/or Phosphoric acid and/or Potash. If the soils are low in one or more of the concerned nutrients, application of that nutrient in a full dose to the soil, will increase the crop yield. If the nutrients are present in a medium amount, only half the dose of that nutrient is applied to the soil.

Different crops require different amounts of nutrients. Vegetables and sugarcane require very high amounts. A requisite amount of nutrients must be given to the crop if the soil contains low quantities of that nutrient.

The nutrient requirement of dwarf varieties of wheat and paddy are more than those of the tall varieties of wheat and paddy less nitrogen is given to the tall varieties, because they will lodge if they as given the dose of nitrogen meant for dwarf varieties.

3. Time of Application of Fertiliser:

The rate of assimilation of nitrogen by crops is equal to their rate of growth. Crops require less nitrogen immediately after germination because they grow less at that time.

The Crops demand for nitrogen increases from the early growth stage to the flowering stage, when their growth rate increases. Therefore nitrogenous fertilisers should be applied in split doses at least twice; once just before sowing or planting the crop and then about one and half to two months after sowing or planting.

The crops utilize about two-thirds of their phosphatic and potash requirements during their early growth period. So then entire quantity of phosphate and potash may be applied as a basal dose just before sowing the crop.

4. Kind or Fertilisers to be Applied:

Nitrate should not be applied to sandy soil, especially under conditions of high rainfall, because they are readily leached. So nitrate fertilisers are usually not applied to paddy fields where ammoniacal and amide fertiliser (Urea) should be applied.

Ammoniacal and amide fertilisers can be continuously applied to neutral and alkaline soils, but not too acidic soils because they increase soil acidity. Water soluble single super phosphate is best suited for application to neutral soils.

If it is added to strongly acidic or alkaline soil, the water soluble mono-calcium phosphate contained in it is precipitated as water insoluble aluminum and ferric hydroxyl phosphate in strongly acidic soil, and as water insoluble tricalcium phosphate in strongly alkaline soil.

Hence lime and gypsum should be added to strongly acidic soil and strongly alkaline soil respectively, in order to adjust the soil pH to approximately 6.8, at which most of the nutrients are made available to crops.

Citrate soluble bone meal or basic slag should be applied to acidic soils. They will continue to release phosphorus for the growth of the crop during the growing season. Sodium Meta and pyro phosphates should be applied to calcareous soil because they do not react with calcium carbonate.

5. Placement of Fertilisers:

Plant nutrients should be placed in the root zone, so that roots can assimilate them quickly. The fertilisers should come in minimum contact with the soil in order to reduce the fixation of nutrient ions like potassium, ammonium and phosphate.

Acidic soils contain aluminum and ferric ions, which precipitate water soluble/phosphate as water insoluble phosphate. Phosphate is also fixed by aluminum, iron oxide and kaolinite. Phosphate ions also move very slowly from their place of application.

Hence single super phosphate or di-ammonium phosphate should be placed in a band at a distance of about two inches from the rows of seeds. In order to prevent weeds from using the fertilisers, nitrogenous fertilisers should also be placed in a band near rows of widely spaced crops.

The uptake of phosphate from the band by the crop increases if the fertiliser band also contains nitrogenous fertiliser.

Roots of closely spaced crops like wheat evenly permeate the soil, so nitrogenous fertilisers may also be uniformly scattered over the surface.

Ammoniacal fertilisers like ammonium sulphate di-ammonium phosphate etc. should be placed in the reducing zone (about nine inches deep) of paddy soil where they remain as ammonium ions which are assimilated by the crop.

If they are placed in the surface oxidizing zone, they are oxidized to nitrate which more down to the reducing zone where they are reduced to oxides of nitrogen and nitrogen gas, which is lost to the atmosphere.

Methods of Application of Fertilisers:

Broadcasting, localized placement and spraying of fertiliser solution on crops are the three main methods of fertiliser application.

1. Broadcasting:

Broadcasting of fertilisers means the uniform spreading of fertiliser over the entire field. It proves effective when the roots uniformly permeate the soil, when heavy doses of nitrogenous and potassic fertiliser are to be applied, and when citrate soluble phosphatic fertilisers like bone meal and basic slag are to be applied to the acidic the soil.

In India, cultivators broadcast the fertilisers on the field and incorporate them in the soil by ploughing. Thereafter the field is thoroughly prepared and seeds of the crop are sown.

Broadcasting of fertilisers (usually nitrogenous) over the standing crop is known as top dressing. The only advantage of broadcasting is that fertilisers may be more conveniently applied in the hilly regions by this method. Fertilisers are also broadcast on grasslands.

Broadcasting of fertilisers should be discouraged due to the following disadvantages:

(i) Most of the plant nutrients are assimilated by weeds.

(ii) Since fertilisers come in contact with a large volume of soil, most of the nutrients, especially phosphates, are fixed up.

(iii) Nutrients cannot be fully assimilated by the roots of widely spaced crops.

2. Localized Placement:

The localized placement of fertilisers means their application very near the seed or the plant. Drill placement of fertilisers means the placement of fertilisers in the soil with the help of drills, which usually have separate seed box and fertiliser hoppers with drills attached, so that the seed and fertilisers are put in same furrow.

The fertilisers, if placed a little below the seed, will not harm the seed and the tender roots of the young seeding. Roots will also develop deeper. Drill application saves the cost of labour.

Plough sole placement of fertilisers means the application of fertilisers in a continuous band at the bottom of the furrow when the field is being ploughed, with a furrow turning plough. This method encourages the development of a deeper root system, because fertilisers have been placed in the moist sub soil where roots develop.

3. Band Placement:

The fertiliser is placed by the side of the crop, either along the row of crops or in the hill near each plant. This is called Band Placement, where the fertilisers are placed to one or both the side of the row of the crop plant at a distance of 2.5 cm to 7.5 cm from it.

4. Spot Placement:

This means the placement of fertilisers at the base of each pair of crop plants.

Advantages of Localized Placement

(i) The fixation of nutrients, especially phosphate, is considerably reduced because the fertiliser comes in minimum contact with the soil.

(ii) The nutrients are near the root hairs which can easily assimilate them, yet are not injured by the high concentration of fertilisers.

(iii) Plough sole placement of fertilisers encourages a deeper root system because the fertiliser is placed in the moist deeper layers where roots readily extend to assimilate the nutrients.

(iv) In the fertiliser band, the high ion concentration facilitates their movement in the roots.

(v) The residual effect of bands of fertiliser is more than that of the broadcasted fertilisers.

5. Spraying of Fertiliser Solutions:

Dilute solutions of nitrogenous and micro nutrient fertilisers are sprayed on the crops and leaves readily absorb the nutrients.