Fertilization: Why is it important to know the Ntotal and NO3 data?

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Sebastian asks: Dear Gustavo. I ask you some questions: 1) In a soil analysis, what use is the data for Ntotal and NO3 (only, not N-NO3)? How can I transform them into something that works for me?

2) In Vertisols from Entre Ríos, it is said that there is a response to N because even though there is a lot of organic matter, it is not very labile. So what would be the usefulness of the data? Would it be useful to estimate the contribution of N, S, P etc. by mineralization?

Response from Gustavo Ferraris: Hello Sebastian, here are my answers: 1) The total N of idea of potentially mineralizable N, because most of it is organic.

Usually, it is about 5% of the organic matter. It does not have a direct relationship with Nitrates. Of the nitrates, by the stoichiometry of the anion in 22.5% it is N and the rest O (oxygen). That is why the Nitrates data is divided / 4.43 to calculate how much N really is. Most laboratories today express the data as N-Nitrates, which is what really matters. Oxygen is superabundant in the atmosphere. The N-NO3 data is very important, because it is the available form that plants assimilate.

2) From a chemical point of view, organic matter (OM) is more protected in a soil with a fine texture compared to another with coarser particles. In other words, 3% in Entre Ríos may be little, but it is a lot, almost a pristine condition for the Central West of Buenos Aires, La Pampa or the South of Córdoba. That is why it is better to relate it to the textural fractions, calculating indices: MO / clay or MO / (clay + silt).

OM is the main property of a soil. Not only does it affect the mineralization of numerous nutrients, such as N, S or Boron (B), to a lesser extent P. It also affects the physical (density, porosity, infiltration, water retention and maximum useful water) and biological properties of the soils.

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