Nitrogen related Point Wise Notes For Competitive exam



• Nitrogen constitutes about 78% of the atmospheric gases.

• Most of the N in soil is in organic form (95 to 99%).

• Total N in Indian soils vary from 0.02 to 0.1%.

• Value of total N in hill soils vary from 0.01 to 0.319%.

• Only about 1.5 to 3.5% of the organic N of soil mineralizes annually.

• Soils in India except those in the hills are generally low in organic matter and total N due to high temperatures.

• In mineralization process, organic N in soil organic matter is converted into plant-usable inorganic forms (ammonium and nitrate).

• Inorganic forms of N in soil include ammonium, nitrate, exchangeable ammonium and fixed ammonium.

• In well-aerated soils nitrate-N is the dominant form.

• Under anaerobic conditions ammonium is the dominant form.

• Nitrogen is taken up by crop plants as nitrate (NO3-) or ammonium (NH4+) ions.

• Most crop plants will equally take nitrate and ammonium.

• Rice is reported to prefer ammonium than nitrates.

• In rice ammonical and amide fertilizers are applied.

Wheat prefer more ammonium at early growth stages and nitrate at later growth stages.

Nitrogen interacts positively with all plant nutrients.

Haber and Bosch first synthesized ammonia from N and H.

• Ammonia synthesis by Haber-Bosch process is carried out at a temperature of 1000 °C to 1200°C and at 200 to 100 atmospheres pressure.

• Industrial fixation (fertilizer nitrogen) by Haber-Bosch process is estimated at about 150 million tonnes per year by 2015.

• Global estimates of biological nitrogen fixation (BNF) are at 175 million tonnes per year.

Anhydrous (without water) ammonia contains 82% N.

• Ammonia is the most reduced form of reactive nitrogen and most abundant alkaline constituent in the atmosphere.

• Urea was the first organic compound to be synthesized from inorganic materials.

• Urea was first separated from urine by Roulle in 1773, hence the name urea.

• In India, the first urea plant was set up in 1959 at Sindri in Bihar.

• About 80% of fertilizer N is consumed as urea.

• Nitrogen content in urea super granules is 46%.

• Urea is used as a substitute for protein in animal feed.

• The permissible limit of biuret in urea is 1.5% as per Fertilizer Control Order.

• Highest permissible concentration of urea in the spray solution for foliar spray is 3% beyond which the leaves get scorched.

• Plant leaves turn yellow due to N deficiency, because N is an important component of chlorophyll.

Cereals remove 20-27 kg N, 8-18 kg P2O5 and 20-40 kg K2O per tonne of grain harvested.

• For producing each tonne (1000 kg) of wheat, the crop removes 25 kg N/ha.

Nitrogen content in rice grains is lesser than wheat grains.

• The first nitrogen fertilizer used was sodium nitrate containing 16% N.

Sodium nitrate also known as nitrate of soda or Chilean nitrate is considered as the first natural mineral containing fixed N and the only natural source of nitrate N.

• Ammonium nitrate contains 32 to 37.5 % N.

• Ammonium nitrate is hygroscopic.

• In calcareous soils, losses from ammonium nitrate are much less than from ammonium sulphate and urea.

• Ammonium sulphate contains 20.5% N.

Organic N content of soil increases steadily with the application of ammonium sulphate.

• Ammonium sulphate nitrate contains 26% N.

• Ammonium sulphate nitrate is an acid forming fertilizer.

• Ammonium chloride (NH4Cl) contains about 26% N and is equally effective as ammonium sulphate for rice.

Potassium nitrate contains 13.8% N and 36.5 % K.

Calcium nitrate contains 15.5 % N and 19.5 % Ca.

• Calcium ammonium nitrate (CAN) is produced by mixing Ammonium nitrate and calcium carbonate.

CAN is produced in two grades containing 20.5% N and 25% N.

• In CAN half of the nitrogen is in nitrate form and half of the nitrogen is in ammoniacal form.

CAN is a neutral fertilizer.

• For alkaline soils, acid forming fertilizers and calcium containing fertilizers are preferred.

• During mineralization, ammonium is converted into nitrate by Nitrosomonas bacteria.

• In rice, percolation losses are 60 to 70 per cent of total water requirement.

• Nitrogen fertilizers are highly soluble in water, therefore subjected to leaching.

• Nitrates are subjected to leaching and nitrification losses in submerged soils.

• Leaching of N in the form of NO3- beyond soil profile is one of the major loss mechanisms that can be as high as 80% depending on the soil properties and water and nutrient-management practices.

• To reduce leaching losses solubility of nitrogen fertilizers is reduced.

• Inherently less soluble nitrogen fertilizers are Isobutylidene diurea (IBDU) – 32.2% N, Crotonilidene diurea – 32.5% N.

• Sulphur coated urea, shellac coated urea, neem coated urea are barrier coated nitrogen fertilizers.

Borax, gypsum and nimin coatings reduce the rate of N release from prilled urea in lowland rice. Borax is effective and increases the productivity of rice.

• A major portion of N fertilizer applied to soil is lost through volatilization as gaseous ammonia.

Loss of N due to ammonia volatilization from agricultural field in India is estimated at 4.1 million tonnes.

Denitrification is sequential reduction of NO3- to N2 by denitrifying bacteria under anaerobic conditions.

Loss of N due to denitrification from agricultural field in India is estimated at 3.1 million tonnes.

• On an average, denitrification losses reported in India ranged from 10 to 30 and 5 to 10 kg N/ha in rice and wheat respectively.

Denitrification is controlled by soil moisture, redox potential (Eh), temperature, pH and substrate (NO3, NO2, NO and N2O) concentrations.

• N losses due to denitrification are likely to be most under alternate flooding and drying as obtained under aerobic rice systems.

• Agriculture sector contributes more than 80% of total anthropogenic NH3 emission to the atmosphere.

• Application of N fertilizer in soil contributes more than 25% of the total NH3 emission from agriculture.

• Current crop removal of N in India is estimated at 9.8 million tonnes.

• Apparent recovery of fertilizer N applied to rice in India is 30-40%.

• Recovery efficiency of fertilizer N in crop production is about 30-60%.

Deep placement of fertilizer N increases its use efficiency.

Nitrification inhibitors are chemicals that inhibit or retard oxidation of ammonium to nitrate N.

 • Nitrapyrin, AM and DCD are the most widely used nitrification inhibitors.

• Growing of crops especially maize increases the release of inorganic N – forms.

Loss of nitrate nitrogen from the soil is less in the presence of maize.

• Urease inhibitors reduce the rate of hydrolysis of urea to ammonium and can reduce loss of N due to ammonia volatilization when urea is surface applied.

• Examples of urease inhibitors are phenyl phosphorodiamidate (PPDA), amino thiosulphate, hydroquinone, phosphoric triamide, cyclohexyl phosphoric triamide, thiophosphoryl triamide, N-(n-butyl) thiophosphoric triamide.

• Adoption of best management practices improves nitrogen use efficiency.

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