Good question, both nitrate and ammonium are very dynamic and the values keep on hanging on the basis of soil edaphic environment. There is no definite relationship between two of them. In aerobic soils, nitrate is generally very high compared to ammonium (eg at the time of sowing of wheat in india nitrate is generally around 12 ppm in surface layer whereas ammonium may be around 2-3 pmm) and in anaerobic soils say for flooded padded transplanting, it may be reverse, ie ammoinum will be around 12-13 ppm and nitrate may be around 2 ppm. Most of the soil testing values are total nitrogen and available nitrogen, and mineral nitrogen is not measured, which is a measure of nitrate and ammonium and we have to derive pedo-transfer function for computing these values for use in DSS and crop models for yield estimates and natural resource management for sustainable agricultutre. There is a need to work for predicting these values on priority basis. As the texture becomes heavier the mineral N is generally high, with higher Organic carbon, the mineral N is generally higher

 regards

Hi, thank you so much. I have this trouble because I have only total nitrogen, but not ammonium and nitrate in soils, values that are important for my crop model. If I understood well, there is a way to derive those values with pedo-transfer functions, is there any publication of how to do it. That can be a way to solve my problem since what I am using until now is sort of a proportion 2:1, but it does not seem to be correct. Many Greetings

TN is the sum of Ammonium, Nitrate and Nitrate

so you have 3 variables not only 2

but if you have measurment for the same area you can collorate it but I dont think there is a direct equation for both of them

please refer to this discussion it may helps you

https://www.researchgate.net/post/Can_I_take_total_nitrogen_TN_as_sum_of_Nitrate_Nitrite_and_Ammonium

yes ,i agree with Dr.mohamed  hassaan

"Total nitrogen" should be the total nitrogen.  That is, including all the organic forms and the mineral forms (nitrate, nitrite, ammonia, ammonium).

However, it's possible that the data you have measured only mineral forms and mislabeled it "total nitrogen".

For optimal uptake and growth, each plant species requires a different ammonium/nitrate ratio. The correct ratio to be applied also varies with temperature, growth stage, pH in the root zone and soil properties. Therefore,the conclusion is that at higher temperatures applying a lower Ammonium/Nitrate ratio is advisable.

At lower temperatures Ammonium nutrition is a more appropriate choice, because oxygen and sugars are more available at root level. In addition, since transport of Nitrate to the leaves is restricted at low temperatures, basing the fertilization on Nitrate will delay the plant's growth. As we already established, sugars need to be transported down from the leaves to the roots to meet the Ammonium. In growing fruits and plants in which the majority of the growth is in the leaves , sugars are consumed quickly near their production site and are much less available for transport to the roots. Thus, Ammonium will not be efficiently metabolized and use of a lower Ammonium/Nitrate ratio is preferred. Also, that uptake of Nitrate increases pH around the roots while uptake of Ammonium decreases it. Ammonium is a cation (positively charged ion), so it competes with other cations (Potassium, Calcium, Magnesium) for uptake by the roots. An unbalanced fertilization, with too high Ammonium content, might result in Calcium and Magnesium deficiencies. Potassium uptake is less affected by the competition. As already mentioned, Ammonium/Nitrate ratio may change the pH near the roots. These pH changes may affect solubility and availability of other nutrients.