1. Please anyone tell me if I analyse my soil nitrogen through CHNS analyser and I get my reading in N% and according to the calculation if my reading is 0.07% then:
N Kg/hectare = 0.07*10000*2.24= 1568 kg/hectare which is too high in field soil sample.
So, please anyone tell what is the exact formula to convert field soil N% into kg/hectare if the sample was analysed through CHNS analyser.
Your calculation is correct. In Indian mineral soils, available nitrogen is generally found low.
1568 kg available N per hectare might be possible if soil is organic or heavily fertilized before sampling. Secondly, Some error might have occurred during analysis. Also, if you are analyzing total N in soil, this figure may be correct because total N is about 10 times higher than available N or more.
Thanks sir for the answer, Yes it is total N but I want to show this data in the manuscript which is 10 times higher.
I'm not sure what the 2.24 factor is, but the conversion from % as analysed to a hectare basis assumes a certain soil mass/ha, i.e. this factor relates to the bulk density and the depth.
Dear Tarun Kumar ,
assuming the your N % is in wt.%, 0.07 % means 0.7 gN / kgsoil.
If we further assume a top soil depth of 0.3 m, an area of 10,000 m2/ ha and a soil density of 1,600 kg / m3, then the N content per ha can be calculated as indicated by Paul Milham :
N (g/ha) = 0.7 gN / kgsoil x 1,600 kgsoil / m3 x 0.3 m x 10,000 m2/ ha = 3,360,000 g / ha = 3,360 kgN / ha.
That suggests that your calculation is principally correct in terms of order of magnitude, which was also confirmed by Girijesh Kumar Sharma . I always recommend my students to carry out calculations with units. That way they can be more confident in their results.
As mentioned by Girijesh Kumar Sharma , CHNS analysis measures the total N content. 0.07 wt.% is close to the lower detection limit of the CHNS analyser, so there are already uncertainties involved in the measurement.
You also need to state the depth of soil sampling (I assumed 0.3 m). If you collected soil at a depth of 0.1 m, the influence of fertilizer applied by top-dressing on the result is greater than if you sample at 0.3 m depth.
Did you collect a composite sample, or just a spot sample? Spot samples are not reliable because it could be possible that the spot was 'contaminated' with inorganic (excessive NPK) and/or organic fertilizer (e.g. chicken litter). Remember, fertilizer is not evenly spread across the field, so you can get fertilizer hot-spots.
If legumes were planted in the field, you may have sampled soil with roots from the legumes that contain high N concentrations produced by N-fixing rhizobacteria.
Hope this helps?
Kind regards, Rob.
Thanks to all and special thanks to Dr Robert Thomas Bachmann to clarify with the calculations.
The sample was collected from 0.3 m depth before any addition of fertilizer and I get 0.07 N% which is lower in range as indicated by Robert and the chances of CHNS analyser error was also effects.
So, In India for the wheat experiment, optimum N required is 120-170 N kg/hectare and according to the CHNS analysis soil N is already too much high.
So, please tell me it is possible to calculate available N kg/hectare from N% in soil.
Dear Tarun Kumar ,
before answering your latest question I would like to confirm that the total value we got for your soil is within the range reported by Niels H. Batjes (Article Total Carbon and Nitrogen in the Soils of the World
). Table 4 reports a range of 1,500 to 21,000 kg TKN / ha.Probably the most accurate way to know the amount of available N would be to extract soil with 2M KCl (Article Nutrient constraints to tropical agroecosystem productivity ...
) and analyze for NH4-N and NO3-N colorimetrically following the procedure ofArticle Tropical soil biology and fertility : a handbook of methods ...
.Alternatively, you need to assume a certain fraction of the total N, that is available to plants for uptake. Refer to Girijesh Kumar Sharma who mentioned that around a tenth of the total N is available. This value agrees well with Li Qian et al. (2014; Article Biochar compound fertilizer as an option to reach high produ...
) who determined total N = 3.08 g / kg and available N = 0.21 g / kg for their soil.
Dear Tarun Kumar ,
before answering your latest question I would like to confirm that the total value we got for your soil is within the range reported by Niels H. Batjes (Article Total Carbon and Nitrogen in the Soils of the World
). Table 4 reports a range of 1,500 to 21,000 kg TKN / ha.Probably the most accurate way to know the amount of available N would be to extract soil with 2M KCl (Article Nutrient constraints to tropical agroecosystem productivity ...
) and analyze for NH4-N and NO3-N colorimetrically following the procedure ofArticle Tropical soil biology and fertility : a handbook of methods ...
.Alternatively, you need to assume a certain fraction of the total N, that is available to plants for uptake. Refer to Girijesh Kumar Sharma who mentioned that around a tenth of the total N is available. This value agrees well with Li Qian et al. (2014; Article Biochar compound fertilizer as an option to reach high produ...
) who determined total N = 3.08 g / kg and available N = 0.21 g / kg for their soil.
N (g/ha) = gN / kg soil x soil bulk density ( kg / m3) x depth (m) x area of hectare (m2)
N kg Per Ha = .07/100×Bulk density of the soil ×Volume of the soil in 1 ha.
Volume = Area (10,000m sq) ×Soil depth . The soil depth depends on the crop under consideration. A rooting depth of 0.3m may be used for most annual crops!
Just wanted to run through the calculation using the 22.4 assumption
Kg Soil per hectare
Kgsoil/.ha = bulk density (g/cm^3 )* soil depth( cm) *1Kg/1000g * 10^8 cm^2/ha
Kg soil/ha = 22.4 *10^5 Kg
Only if
Bulk Density = 1.32 g/cm3
Soil Depth = 17 cm
0.07% = 0.7g/Kg
Therefore 0.7g/Kg * 22.4 [10^5] = 15.68 * 10^5 g/ha
15.68 [10^5]kg/ha * kg/1000g = 1568Kg TN per ha
Stated analysis was by a CHNS analyzer therefore N is as Total Nitrogen rather than available.
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