Fate And Reaction Of Various Fertilizers In Soil.

There are five major processes that happen to applied fertilizer after applying it in the field:

1. It is taken up by the crop.
2. It reactes with soil minerals amd organic matter to become part of the soil reserve.
3. It can leach from the root zone with water.
4. It can move from the field through soil erosion and and water runoff.
5. It can be lost to the atmosphere as a gas.

Fate and reaction of nitrogen fertilizers:

Nitrogen fertilizers can be subject to all five of these processes and may be the most difficult to manage of all nutrients. Nitrogen fertilizer is most commonly added in the form of nitrate, ammonium or urea. Their behaviour is quit different and they need to be managed with their specific properties in the mind.

Nitrate: Nitrate is very soluble in the soil and moves freely with water in the soil. Excessive rainfall or irrigation can easily move nitrate below the root zone. In wet soils, bacteria may convert nitrate to nitrous oxide (N2O), causing a loss of valuable resource and the production of green house gas. Nitrate can also be converted to inert N2 gas.

Ammonia: As a positively charged cations, ammonium is largerly held on soil cation exchange sites. In warm aerated soils, ammonium is converted in to nitrate with a few days or weeks. In flooded soils, ammonium can persist for long peroids of time. When left on the soil  surface, ammonium is in equilibrium with ammonia gas & can be lost to the atmosphere.

Urea: As a non charged molecule, urea moves freely with water in the soil. In warm soils, urea is decomposed to ammonium with a week or two by an enzyme (Urease) that is present in almost all soils and plants.When urea is left on the soil surface a portion of the ammonium will lost as ammonia gas. If Urea is placed below the soil surface will washed into the soil by rainfall, ammonia losses are very low.

All added N fertilizers is accessed by soil microorganisms before the plant roots have a chance for uptake. Since there are between 100 million to 1 billion bacteria in a single teaspoon of soil, their number in an entire acre are almost unimaginable. When canditions are optimal, microorganisms will immobilize some of the N in their cell and it will become part of soil organic matter.

(Immobilization is a process that lead to change of soil inorganic N into organic forms.)

Phosphatic Fertilizers: These doesn't take much time to react with soil to form many new compounds and remains very close to where it is applied. The most common phosphate Fertilizers are DAP, P2O5 and monoammonium phosphate (MAP).

Phosphate fertilizers are initially soluble in the water and thus readly used by plants but they quickly react with clays and other elements in the soil to become less soluble. These newly formed compounds will slowly dissolve and release soluble P over many months or years. These chemical reactions can be influenced by modifying the fertilizer properties or by minimizing fertilizer contact with soil with banded fertilizer application.

Since P Fertilizers are tightly bound to soil particles, erosion from the field in runoff water can be pathway of loss. Added phosphate fertilizer is incorporated in to microbial biomass and soil organic matter, but smaller amounts than N Fertilizers.

Pottassic Fertilizers: These are most commonly added as potassium chloride (KCl)

However all forms of K fertilizer contain the identical chemicl form K positive. Other K containing Fertilizers may contain nitrate, sulfate, thiosulfate or phosphate, but the behaviour of the K will be the same. Potassium is simpler to manage than N and P since it is not involved in biological transformations. Most K fertilizers dissolve quickly in the soil and the K will either immediately displace another cation on the clay surface or move with water untill it displaces another cation.