@ Kunal, ammonia is prone to loss by volatilization from soil during N application or converted to nitrate by nitrifying bacteria present in the soil as well as nitrate is very prone to leaching. Therefore, you may get more nitrate than ammonia in your field leachate.

Ammonium being a cation is adsorbed on clay complex and is thus not prone to losses via leaching. It is primarily lost via ammonia volatilization. On the other hand, ammonium-N is rapidly converted to nitrate-N (under aerobic conditions) and being an anion, nitrate-N moves along with water percolating down the soil profile. So in the field leachates, it is expected that there will be more nitrates than ammonium-N

For Konal: ammonia is volatile , nitrates are not,so we always find more nitrate that ammonia.

Ammonia is usually hold by cation exchange capacity, while the capability of soil colloids to hold anions (such as nitrate), is much more limited.

One needs also to consider the daily timing, the season, and the crops that could be present, but, with all factors being equal, the volatilisation of ammonium compounds remains the relevant factor.

Ammonium N loss due to volatilization during N application and Nitrate N loss occur due to negative charge and therefore it concentration is higher in leachate than Ammonium N.

The above answers are correct in most respects. However, the high nitrates in leachate are due to rapid conversion of ammonium in the solution to nitrate. Ammonium will not volatilize unless it is at or on the soil surface and the soil pH is well above pH 8. The log Ko of ammonium is 9.28 meaning that at pH 9.28, one-half of the ammonium is in the ammonium form and one half is in the ammonia form (i.e., volatile). Due to the ammonium attaching to exchange sites on the clay minerals and organic matter it will not volatilize from below the soil surface under normal soil conditions unless the soil is extremely alkaline. The rapid biological conversion of ammonium to nitrate results in most of the mineral N residing as nitrates in the soil both as a result of natural N mineralization from SOM and from applied fertilizers. Thus, most of the N resides in the nitrate form in the soil solution and is expressed as such in leachates.

Bcz it is more mobile than Ammonium.

Kunal . Bijay Singh Larry Cihacek

As already mentioned by many RG members above, it is largely related to the positive charge of ammonium and negative charge of nitrate which makes nitrate very mobile in the soil but not ammonium. This is particularly true for temperate soils (and young tropical soils) dominated by layer silicate clays with a negative net charge. Another important reason as Professor Cihacek has pointed out is the rapid conversion of ammonium to nitrate in the solution. However, the mobility of both ammonium and nitrate ions could be different for the highly weathered tropical soils (Oxisols and Ultisols) dominated by oxide clays many of which have zero or positive net charge depending on their soil pH. Under such conditions, there could be heavy leaching of both ammonium and nitrate ions or ammonium alone if the soil has a net positive charge.

Ammonium is complexed by soil clay and organic colloid while nitrate is highly labile because it can't be adsorbed by colloids in soil

Firstly,

Tendency to form nitrate from ammonium in soil system is very high. That is why most of the nitrogen get converted to nitrate in soil by microbial oxidation( Nitrosomonas and Nitrobacter).

secondly,

Being a very soluble and labile form of nitrogen it easily get dissolved and subsequently leached down in the deeper soil. Naturally the fraction of Nitrate is found to be high in the leachate.

Thirdly,

Being an anion it easily get leached . On the other hand, ammonium being a cation get absorbed in the soil colloidal system and got restricted.

( N.B- Soil colloidal system mostly an anionic system , that is why it can form complexes with cations present in soil system).

Thanks & Regards

Debashis Dutta

ammonium in soil system is instabilizing. the N from NH4+ is -3, it is easy to loss the electron.

Nitrate will be formed by nitrification process from ammonia. Since nitrate ion has negative charge which cannot adsorbed on clay complex and further it gets leached down along with percolating water. Ammonia lost by volatilization process and ammonium ion due to its positive charge adsorbed on clay complex.

Thanks to all the colleagues for their answers, nitrate ion and clay have negetive charge and and repulse each other, it can easily soluble to water Therefore, it is leached and is more common in drained waters.

Ammonium nitrogen is an assailable form of nitrogen and ready for incorporation into biological systems through various biochemical oxidation reactions. These reactions generate along with the leachate especially in waste dump sites, higher oxidation states of nitrogen like the nitrates referred to in the question. Plants especially crop plants require nitrogen in the nitrate form because of their tremendous nitrate reductase activities. Therefore leachate in itself could serve as a ready source of manure to encourage crop production.

Kunal . Have a look of the article in the attachment. It might help you.

Nitrification is the process that converts ammonia to nitrite and then to nitrate and is another important step in the global nitrogen cycle. Most nitrification occurs aerobically and is carried out exclusively by prokaryotes. Ammonia is prone to loss by volatilization from soil during N application or converted to nitrate by nitrifying bacteria present in the soil as well as nitrate is very prone to leaching. Therefore, you may get more nitrate than ammonia in your field leachate. However, consuming too much nitrate can affect how blood carries oxygen and can cause methemoglobinemia. Therefore, water is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients