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List of commonly used fertilizers: 1. Nitrate Fertilizer 2. Phosphatic Fertilizers 3. Potassic Fertilizers 4. Micronutrient Fertilizers 5. Nitrification Inhibitors and Slow Release Fertilizers 6. Bio Fertilizers/Microbial Inoculants.
1. Nitrate Fertilizer:
Highly mobile in soil, suitable for top dressing, highly soluble and subjected to leaching and denitrification in water logged soils, increase alkalinity, more suitable for dry soils.
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Ammoniacal Fertilizer:
Readily soluble in water, less leaching losses as NH+4 are adsorbed on clay complex, suitable for water logged fields, acidic in nature; paddy in early stage is capable of utilising NH+4 form.
Amide Fertilizer:
Organic fertilizer, first converted into ammoniacal and then to nitrate form. Urea is acidic but CaCN is basic. Highly soluble in water.
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Amide → (NH4)2CO3 → NO–3
Nitrate-Ammoniacal Group:
NO3– nitrogen readily available to plants for rapid growth and NH4+ nitrogen at the later stage.
1. Sodium Nitrate:
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16% N, Chilean nitrate, pioneer nitrogenous fertilizer; useful for acidic soils. Its continuous and abundant use causes deflocculation and develop a bad physical condition in low rainfall regions.
2. Ammonium Sulphate:
20.6% N and 24% S. 20 times less used than urea. During rainy season, it sometimes forms lumps, suitable for paddy and jute .Maximum moisture by wt. = 1%, Arsenic oxide- max.0.01%, Ammoniacal Nitrogen: 20.6% by wt.
During fixation, NH4+ releases an equivalent quantity of Ca2+ from the soil and CaSO4, that results, is leached away under humid conditions. Application of (NH4)2SO4 reduces the quantity of reserved calcium in soil. If there is no reserve of Ca in the soil, the H2SO4 is formed as a residual product which will increase the acidity in soil.
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3. Ammonium Nitrate:
33-35%N, highly hygroscopic and not fit for storage, liable to explode.
Nitrochalk is less hygroscopic and formed by mixing amm.nitrate with about 40% limestone or dolomite, useful for acid soils.
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4. Amm. Sulphate Nitrate:
26% N, 15%S, It is a mixture of Amm. sulphate + Amm. Nitrate. Three- fourth of N is in ammoniacal form.
5. Calcium Ammonium Nitrate (CAN):
Kisan Khad, 25-28% N (mostly 26%) almost neutral in nature, most suitable for vegetables, commercially prepared from amm.nitrate and ground limestone, half of N is in ammoniacal form. According to standard, moisture content by wt. < 1%, calcium nitrate < 0.5% by weight.
6. Ammonium Chloride:
26% N, extensively used in paddy in Japan. It is usually not recommended for tomatoes, tobacco etc. Cereal crops are not affected by CI– as most of it is retained by straw and is not translocated to the grain. In some crops like potato and sweet potato high quantity of CI– is avoided and instead K2SO4 or KNO3 is used (KNOs: 13.85% N and 46-47% K2O).
7. Urea:
It is mostly used in India, 46% N, fairly hygroscopic therefore produced in granular or pellet form and is coated with a non-hygroscopic inert material. Max.moisture – 1% by wt. and Biuret – < 1.5% according to fertilizer control order.
Biuret is formed during manufacturing of urea when temp, goes high above 150°C and is toxic to plants when its concentration is more than 2%.
The whole conversion takes about 4-7 days. Therefore it is advisable to apply Urea 3-4 days before sowing.
8. Cyanamide/Nitrolim/Cal.Cyanamide:
20.6% N, certain immediary compounds formed during its decomposition injure tender and germinating seedlings and therefore it is advisable to apply it at least a week before sowing. Lime is one of the products of decomposition and a certain amount of lime is also present in the original material and these are of high value in acid soils.
9. Aqueous Ammonia:
80%N, used as fertigation i.e. in irrigation water.
2. Phosphatic Fertilizers:
It is of 3 types, namely:
(A) Water Soluble:
Ca(H2PO4)2 such water soluble phosphatic fertilizers are used for quick start and short duration like wheat, for neutral and alkaline soils e.g.-
1. Super phosphate is of three types-
(i) Single super phosphate – 16-20% P2O5
(ii) Double super phosphate – 32% P2O5 (25-30%) or Enriched super phosphate
(iii) Triple super phosphate – 46-48% P2O5 (44-52%)
2. Monoammonium Phosphate (MAP) – 12%N and 48% P2O5
3. Diammonium phosphate (DAP) – 16-48-0; 18-46-0,
(N → P2O5 → K2O)
(B) Citrate Soluble (but Water Insoluble):
Ca2H2(PO4)2 or Ca2(HPO4)2 used in acid soils, for long duration crops like sugar cane, low land rice, tapioca & tea. e.g. –
1. Dicalcium Phophate – 33-40% P2O5
2. Thomas/Basic slag – 14-18% P2O5
3. Rhemania Phosphate – 23-26% P2O5
(C) Citrate and Water Insoluble:
Ca3(PO4)2 Tricalcium phosphate used in strongly acid soils and suitable for plantation crops e.g. –
1. Rock Phosphate – 20-30% P2O5
2. Raw Bone meal – 3-4%N + 20-25% P2O5
3. Steamed bonemeal – 1-2%N + 20-30% P2O5
Single Superphosphate (SSP):
SSP contains 12% S + 16% P2O5 + 18-21% Ca. Among phosphatic fertilizers, SSP is widely used in India. It is prepared by treating Rock Phosphate with equal amount of Sulphuric acid. After treatment dusty coloured mixture of calcium phosphate and calcium sulphate in equal amount is obtained. But SSP is generally formed by the mixing of Mono calcium Phosphate and Calcium Sulphate (Gypsum) in both forms i.e. powder and granular.
In alkaline or acidic soils SSP forms Calcium Phosphate, Iron phosphate or Aluminium phosphate, thereby preventing the fertilizer loss with water and thus is solublised slowly in soil. That’s why total amount of this fertilizer is applied as a single dose either at sowing/planting time or before the time of sowing/planting. In general, SSP is suitable for all the crops and different soils.
According to standard; SSP must contain:
Dicalcium Phosphate:
By neutralising the phosphoric acid by lime, Dicalcium phosphate is prepared and phosphoric acid is obtained by reacting HCI, H2SO4 or HNO3 with rock phosphate.
This fertiliser is equally suitable for acidic neutral and alkaline soils but it is especially useful for acidic soils because it does not form compounds in such soil.
3. Potassic Fertilizers:
K- Containing minerals are primary minerals like feldspar/or- thoclase, Muscovite and Biotite.
1. Muriate of Potash (MOP):
KCl; 60% K2O, Na as NaCl by wt. less than 3.5%, min 58% K2O. It is not used in tobacco, rice, tomato, sugarcane, beets and starchy crops. In sugar crops accumulation of sugar is affected by CI–. Higher content of CI– in tobacco leaf reduces its burning quality. Although MOP is highly soluble in water but is not lost by water because it is adsorbed in the soil lattices.
2. Potassium Sulphate or Sulphate of Potash (SOP):
48-52% K2O and 17-18% S. suitable for light soil and for those crops for which MOP is unsuitable.
3. Nitrate of Potash (NOP) /Potassium Nitrate (KNO3):
13% N, 44% K2O, excellent source of K and N; mainly used for fruit trees and crops such as tobacco and vegetables.
4. Micronutrient Fertilizers:
Some of the metallic micronutrient salts when applied to the soil, are transformed into non-available forms due to their reactivity. Organic compounds like EDTA (Ethylenediamine tetra acetic acid), DTPA (Diethylene triamine penta acetic acid) CDTA (Cyclohexane diamine tetracetic acid) have the ability to chelate or loosely hold metallic ions in their cyclic structure and these metal-organic complexes are called metal chelates.
Metal chelates are soluble in water but they do not ionise in soil solutions. Metal ions therefore, don’t react with soil constituents. Chelate forms of nutrient are more available. Fe, Cu, Zn and Mn are available in chelate form. 50% of Indian soil is deficient in Zinc and 25% of Indian soil in sulphur.
5. Nitrification Inhibitors and Slow Release Fertilizers:
Among the major nutrients, P & K are less mobile as compared to N. Nitrogenous fertilizers are easily lost by leaching, volatilisation and denitrification. To offset these losses to the minimum, N is applied in split doses at the critical phases of crop growth.
However split application increases the cost of fertilizer application .In order to reduce the leaching, volatilisation and denitrification losses to the minimum, use of some nitrification inhibitors or slow release fertilizers are useful to regulate the nutrient availability to the crop.
Advantages of Nitrification Inhibitors and Slow Release Fertilizer:
(i) They improve the uptake of N by releasing the nutrient slowly and uniformly.
(ii) Labour saving device since no need for split application.
(iii) Scope for reducing the fertilizer dose due to higher efficiency of fertilizer and uptake of nutrient.
(iv) Low pollution of water and air since leaching losses are minimum.
(v) Application of fertilizer can be done either basal or top dressing thereby greater flexibility in timing.
Nitrification Inhibitors:
Inhibitors are used with good results in case of non-nitrate fertilizers such as ammonia, ammonium salt, urea etc. Inhibitors decrease the activity of nitrifying bacteria e.g. –
For Lowland:
(a) Oxamide (NH2CO-CONH2) – 31%N, not hygroscopic, solubility is 0.4g/lit.water.
(b) Dicyandiamide (DD) – NH2C (=NH) NHCN: 42% N
(c) Thiourea (TU) – 36.8% N
(d) Urea pyrolyzate – 48% N.
For Upland:
(a) AM (2-amino-4-chloro-6-methyl pyrimidine)
(b) N-Serve (2-chloro-6-trichloromethyl pyridine).
Others:
(a) ASU (Guanyl thiourea)
(b) Nitrapyrin
(c) ST (Sulphathiazole)
(d) DCS (K) ATC
(e) Neem Cake.
Slow Release Fertilizers:
To overcome the problem of leaching, the solubility of nitrogen fertilizers are reduced by:
(A) Synthesizing compounds which are inherently less soluble e.g.:
1. lsobutylidene diurea (IBDU) – 31-32%N.
2. Crotonylidene diurea (CDU) – 32.5%N.
3. Guanyl urea sulphate (GUS).
4. Urea Formaldehyde (UF/Urea Form) – 38-42% N, less hygroscopic than urea.
5. Oxamide.
(B) Coating barriers to the presently available fertilizers e.g. – Sulphur coated urea, Neem coated urea, and Lac coated or shellac coated urea (34.2% N).
(C) Formation of Super Granules/Modified Form:
Big granules of urea 1-4 g each are made. When these granules are placed in the reduced zone of soil, the losses are substantially reduced. To facilitate deeper placement, Urea is manufactured as super granules, briquettes or mixed with mud and made into balls.
GROMOR/Gromor – Trade name of urea ammonium phosphate grade – 29:29:0.
Ammophos-B – Earlier name of Ammonium phosphate sulphate, grade – 20:20:0.
6. Bio Fertilizers/Microbial Inoculants:
‘Microbial Inoculants’ is the more appropriate name of Biofertilizer. It is defined as preparation containing live or latent cells of efficient strains of N-fixing, PO43- solubilising or cellulolytic micro-organisms used for application of seed, soil or composting areas with the objective of increasing the number of such micro- organisms and accelerate certain microbial process to augment the extent of the availability of nutrients in a form which can be assimilated by plants.
Application:
(a) Seed Inoculant:
20g of Rhizobium culture is required to treat 1 kg seed. One packet of Rhizobium culture contains 200g of Rhizobium culture.
(i) For small seeded pulses like moong , Arhar, lentil, berseem, lucerne, Kulthi, 500g of Rhizobium culture is sufficient for seeds required to be sown in 1 ha i.e. 2.5packets/ha (since 1 packet=200g.)
(ii) For Groundnut, 1. 5kg of Rhizobium culture for 80-100 kg seeds for 1 ha i.e. 7.5packets/ha.
(iii) For soybean and Bengal gram – 1 kg/ha i.e. 5packets/ha.
(b) Soil Inoculant:
10 packets (2kg/ha)of carrier based Azotobacter and Azospirillum culture is mixed with 25kg FYM and 25kg soil and is broadcasted in the field uniformly before transplanting.
Benefits:
1. Rhizobium Biofertilizer can fix 50-200kg N/ha per year.
2. Increases yield by 25-30% and 40-80kg N is left over in the field useful for subsequent crop.
3. BGA can add up to about 20-25 kgN/ha to rice field.
4. BF like BGA, Azotobacter and Azospirillum also supply growth regulator such as IAA, JBA, NAA, GA1 to GA33 and vitamins.
5. Azotobacter and Azospirillum secrete antibiotics which act as pesticides so biofertilizers also act as ‘Bio-pesticides.’
6. Azolla not only supplies N but also increases O.M. inform of biomass and increases soil fertility.
7. It increases soil’s physical properties such as soil structure, texture, chemical properties such as water holding capacity, cation exchange capacity of soil, buffer capacity of soil etc.
8. It proliferates useful soil micro-organism i.e. biological properties of soil.
9. It is ecological friendly, technologically feasible and socially acceptable input to the farmers.
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