Complete List and Importance of Chemical Fertilizers for Crops

January 15, 2023 Agric4Profits

The term “chemical fertilizers” refers to a wide range of synthetic compound substances developed specifically to boost crop yield. Some chemical fertilizers, for example, are “nitrogenous” in the sense that they contain nitrogen, whereas others are phosphate-based. Potassium is found in other fertilizers.

Chemical fertilizers that are complex (or blended) often contain a combination of ammonium phosphate, nitro phosphate, potassium, and other nutrients.

Chemical fertilizers enable farmers to maximize crop yield on a specific plot of land; the more the plant grows, the better.

Fertilizer ensures that each plot of land produces as efficiently as possible.

1) Nitrogenous Fertilizers

Complete List and Importance of Chemical Fertilizers for Crops

Many straight and compound fertilizers contain nitrogen in the form of ammonium (NH4 ions), which is quickly converted to nitrate (NO2 ions) by bacteria in the soil.

Most crop plants, such as cereals, absorb and respond faster to NO3 ions than to NH4 ions, but rice, potatoes, and grasses are equally sensitive to both forms.

Nitrogenous fertilizers are classified into four groups based on the chemical form in which nitrogen is combined with other elements in a fertilizer:

1a) Nitrate Fertilizers

In these fertilizers, nitrogen is combined in nitrate (NO₃) Form with other elements.

Such fertilizer are sodium nitrate (NₐNo₃), having 16 percent N, calcium nitrate [Ca(NO₃)₂], Having 15.5% N and potassium nitrate (KNO), having 13.4%k.

Nitrate fertilizers are quickly dissociated in the soil, releasing the nitrate ion for absorption.

As a result, they are easily absorbed and utilized by plants.

The high mobility of nitrate ions in soil has the advantage of allowing nitrogen to reach the root zone quickly even when applied to the soil’s surface.

As a result, they are frequently used as side and top dressings. However, there is an increased risk of these fertilizers leaching.

All the nitrate fertilizers are basic in their residual effect on the soil and their continued use many reduce soil acidity.

1b) Ammonium Fertilizers

In these fertilizers, nitrogen is combined in ammonium (NH⁺₄) form with other elements examples of such fertilizers:

1. Ammonium Sulphate [NH₄)₂SO₄], having 20%N,

2. Ammonium phosphate(NH₄H₂PO₄) having 20%N and 20% P or 16%N and 20%p;

3. Ammonium chloride (NH₄CI), having 24-26%N,

4. Anhydrous ammonia, having 82%N and

5. Aqueous ammonia having 28%N.

When added to the soil, the ammonium ion is temporarily retained by the colloidal fraction of the soil until it is nitrified.

These fertilizers are much more resistant to loss by leaching because the ammonium ions are readily adsorbed on the colloidal complex of the soil.

Most ammonium fertilizers have an acidic residual effect on the soil.

1c) Nitrate and Ammonium Fertilizers

These are nitrogen fertilizers that come in both ammonium and nitrate forms.

1. Ammonium nitrate (NH₄NO₃), having 32.5%N,

2. Ammonium sulphate nitrate (ASN)[ (NH₄)₂ SO₄NH₄NO₃)], having 26%N,

3. Calcium ammonium nitrate (CAN)[Ca(NH₄NO₃)₂], having 25%N.

These fertilizers are easily soluble in water and can be used in a wide range of soil and cropping conditions.

These fertilizers’ nitrate nitrogen is readily available to plants for rapid growth, while the ammonium nitrogen resists leaching losses and can be used by plants at a later stage. These fertilizers have an acidic residual effect on the soil.

1d) Amide fertilizers

These fertilizers are carbon compounds, and so are called organic fertilizers. Important fertilizers in this group are:

1. Urea [Ca(NH₂)₂], having 46%N and

2. Calcium cyanamide (CaCN₂), having 22%N

These fertilizers are easily soluble in water and decomposed by soil microorganisms.

In the soil, they are quickly converted to ammonia and then to nitrate.

General Recommendation on the Use of Nitrogen Fertilizers

1. Ammonia-forming fertilizers such as ammonium sulphate, ammonium chloride, and urea are recommended for rice.

Ammonium-nitrate fertilizers such as ammonium sulphate nitrate, ammonium nitrate, and calcium ammonium nitrate should be used if these fertilizers are not available.

For the rest of the field crops, all nitrogenous fertilizers are equally effective.

2. Ammoniacal or ammonium-forming fertilizers should be avoided indefinitely on acidic soil because they cause the soil to become more acidic.

3. The best applications for all nitrate fertilizers are side and top dressing.

4. Because they are easily leached, they should not be applied in large quantities in light sandy soils or during heavy rains.

5. Apply the entire recommended dose of nitrogen in two or three separate applications.

2) Phosphorus Fertilizers

Phosphorus is absorbed by crop plants in the form of negatively charged ions such as HPO24 or H2PO4.

Phosphorus fertilizers are classified into three types based on how phosphoric acid is combined with calcium.

Phosphorus fertilizers containing water-soluble phosphoric acid or monocalcium phosphate [Ca (H2PO4)2] include superphosphate, ordinary or single, with 16-18% P2O5; double superphosphate, with 32% P2O5; triple superphosphate, with 46.48% P2O5; and ammonium phosphate, with 20% N and 20% P2O5 or 16% N and 20% P2O5.

Because plants absorb phosphorus as H2PO4 ions, these fertilizers are quickly absorbed by the plants.

Water-soluble phosphoric acid is rapidly converted to water-insoluble phosphoric acid in the soil.

As a result, there is no danger of nutrient loss as a result of leaching.

This group of fertilizers should not be used in neutral, alkaline, or acidic soils.

Phosphoric acid is converted to monocalcium phosphate in acidic conditions, and the phosphate has a lower chance of being fixed as iron or aluminum phosphate.

Fertilizers containing citric acid, soluble phosphoric acid, or dicalcium phosphate [CaHPO4]; examples include basis slag, which contains 14-18 percent P2O5; dicalcium phosphate, which contains 34-39 percent P2O5; and rhenania phosphate, which contains 25-76 percent.

These fertilizers are especially suited to acidic soil.

Fertilizers containing insoluble phosphoric [Ca(PO4)2]: examples of phosphatic fertilizers include rock phosphate, which contains 20-40 percent P2O5; raw bone-meal, which contains 20-25 percent P2O5 and 3-4 percent N; and steamed bone-meal, which contains 22 percent P2O5.

These fertilizers are ideal for strong soils or organic soils that require a large amount of phosphorus fertilizer to increase soil fertility.

Principles of Effective Utilization of Phosphorus Fertilizers

1. Granular fertilizers with a high degree of water solubility outperform powered fertilizers on acid and neutral soils.

2. On acidic and neutral soils, band application of powdered fertilizers with high water solubility outperforms mixing the fertilizers with soil.

3. Water soluble fertilizers produce the best results when applied in a band.

4. To get the best response from phosphorus fertilizers, other nutrients must be present in sufficient quantities.

3) Potassium Fertilizers

All potassium fertilizers consist essentially of potassium in combination with chloride, sulphate , or nitrate. Almost all potassium fertilizers are water soluble.

The following are examples of potassium fertilizers;

1. Potassium chloride [KCI] or potash muriate, containing 60-63 percent K2O

2. Potassium sulphate [K2SO4], containing 50-53 percent and 18 percent sulphur, respectively.

3. Potassium-magnesium sulphate [K2SO4. MgSO4] with a K2O5 content of 22%

4. Potassium nitrate [KNO3], which contains 13% nitrogen and 44% K2O5.

5. Potassium metaphosphate [KPO3], which contains 40% K2O5S and 60% P2O5.

Principles of Effective Utilization of Potassium Fertilizers

1. Because potassium fertilizers are all readily soluble in water, they are all equally available to plants.

2. Because of the presence of other elements, potassium fertilizers containing sulphur, magnesium, or sodium have some additional agronomic importance on some soils.

3. Use potassium fertilizers containing chlorine or sulfur with caution, as they may be harmful to some crops.

4) Compound Fertilizers

Compound fertilizers provide two or three of the major plant nutrients (i.e nitrogen, phosphorus, and potassium).

They are created by combining simple fertilizers such as ammonium nitrate, ammonium phosphate, and potassium nitrate, as well as more complex chemical processes.

The chemical composition of compound fertilizers is typically expressed as a ratio of nitrogen, phosphorus, and potassium expressed as elemental N, P2O5, and K2O, respectively.

A 15:20:10 compound fertilizer contains 15% nitrogen, 20% phosphorus P2O5, and 10% potassium expressed as K2O.

Advantages of Compound Fertilizers

1. The mixture of usually dry, fine and well mixed and can be applied by hand as well as through a fertilizers drill.

2. The mixture usually contains all major plant nutrients.

3. It saves the farmers time and labor.

4. It does not form lumps or deteriorate in any way if it is not used immediately

Grades of Compound Fertilizers

Low grade mixtures are 6:12:6, 5:10:10, and 9:9:0 and high grade mixtures are 15:15:15, 20:20:20. Using high grade fertilizers have some advantages like:

1. Low cost per unit of plant nutrient

2. Lower cost of transportation, labor, and storage

3. Increased the speed of application in the field.

5) Slow Release Fertilizers

Slow or controlled release fertilizers contains a plant nutrient (usually nitrogen) in a form, which-after application-delays its availability for plant uptake significantly longer than a common fertilizers.

This effect is achieved by coating common (nitrogen or NPK) fertilizers with sulphur, a semi-permeable polymer material, or special chemical nitrogen compound formulations.

Advantage of low release fertilizers

1. Labor saving, instead of several split application only one for the whole growing period.

2. Reduce toxicity to seedling even with high application rates

Disadvantage of low release fertilizers

These cost per unit of nutrient is considerably high than that in common fertilizers.

6) Nitrification and Urea Inhibitors

Nitrification inhibitors are compounds that, when added to nitrogen fertilizers (which contain nitrogen in the form of ammonia (NH4+), cause a delay in the transformation of the ammonium ion (NH4+) held by the adsorption complex into nitrite (NO2) and then to nitrate (NO3) through the activities of soil bacteria, thereby preventing leaching of nitrate not immediately taken up by the crop.

Urea inhibitors are compounds that slow the transformation of the amide-N in urea into ammonium for 10 to 12 days, preventing or reducing ammonia evaporation losses to the air when the weather is dry or the urea cannot be incorporated into the soil immediately after application.

Before spreading, both nitrification and urea inhibitors are thoroughly mixed with nitrogen fertilizers and then spread together in the mix.

Calculating the rate of fertilizers to be applied

The amount of fertilizers to be applied per hectare on a given is determined by:

1. The amount of nutrients that a plant requires for optimal growth and productivity.

2. Nutrient availability in the soil (level of soil fertility)

3. The moisture status of the soil

4. The type of crops to be grown

5. The types and grades of fertilizers

Usually mineral fertilizers are delivered in 50-kg bags while the nutrient content (active ingredients) is given in percentages e.g N 15 P 15 k 15. Meaning that each bags 50kg contained 15%N15%P15%P

Steps to follow in calculating the rate of fertilizers to be applied

i. Calculate the amount of active ingredients contained in each bag by dividing the percentage of each nutrient by two.

N15, P15, and K15 are examples of active ingredients.

P15/2=7.5kg K15/2=7.5kg N15/2=7.5kg P15/2=7.5kg K15/2=7.5kg

If the recommendation is to apply N60-P60-K60 per hectare, the farmer’s most convenient option is to purchase N15-P15-K15 nutrient (compound) fertilizer.

N7.5kg-P7.5kg-K7.5kg of active ingredients is contained in one 50-kg bag.

To calculate the number of bags needed to provide the recommended nutrient:

1 bag = 7.5 kg X 60 kg

Find X X = 60 divided by 7.5 = 8 NPK bags.

ii. For example, how many bags of ammonium sulphate (AS) (with 21% N and 24% S) are required to supply 60kg/ha of N?

10.5 is the result of dividing 21 by 2.

As a result, approximately six bags of AS would provide 60.5kg of N active ingredients.

Furthermore, six bags of AS will provide 72kg/ha of sulphur.

To apply the recommended rate of 60kg/ha N60kgP2O5 and 60kg/ha K2O, eight bags of 50kg N15-P15 are required.

iii. When the recommendation per hectare is N60-P30-K30, a farmer would divide 30 by 7.5 to get 50-kg bags of N15-P15-K15 grade.

Because each 50kg contains 7.5kg of NPK active ingredient.

In this case, he should apply four 50kg bags of NPK fertilizer per hectare, with half the recommended rate of nitrogen and the full rate of phosphate and potassium as basal dressing.

The remaining 30 kg/ha N should be applied as one or two top-dressings of straight nitrogen fertilizer following good agricultural practices.