The Soil and Plant Laboratory

Brief descriptions of the analyses we perform at the Soil and Plant Laboratory are listed here below.

Dry matter and loss on ignition

The sample is weighed and dried in a heating cabinet at 105°C for 20-24 h. The sample is then weighed, and the dry matter is calculated. For loss on ignition, the dry sample is placed in a muffle furnace and burned at 550°C for at least 2 hours. The sample is then weighed and the loss on ignition is calculated.

Carbon and nitrogen - determination by Dumas method

Combustion at 1350°C: The sample is burned in pure oxygen at 1350°C. The combustion gases are then analysed for carbon dioxide (CO₂) and nitrogen (N₂).

Total Carbon and Nitrogen: The results are given as the total weight percentage of carbon (Tot C) and nitrogen (Tot N).

Determining Organic Carbon:

Initial heating at 550°C: The sample is first heated at 550°C to remove organic carbon (Org C) and then analysed.

Combustion of Remaining Carbonate Carbon: The remaining carbonate carbon (Karb C) is burned at 1350°C.

Calculation: The organic carbon content is calculated as Org C = Tot C - Karb C.

pH of water extract

Mixing and Shaking: The soil sample is mixed with water and shaken.

pH Measurement: Depending on the technical rule or regulation, the pH value is measured either in the suspension or in the supernatant.

Method Variations: Different methods specify different shaking times and mixing ratios between water and soil.

ISO 10390:2022 Method: This method uses a volume-to-volume ratio of 1:5 for mixing, and the pH value is determined in the soil suspension.

pH of 0.01 M CaCl₂ extract

Procedure as above with exception that the soil sample is mixed with 0.01 M CaCl₂ solution.

pH of 1 M KCl extract

Procedure as above with exception that the soil sample is mixed with 1 M KCl solution.

Acidity of 1 M KCl extract

The sample is extracted with 1 M KCl solution and filtered. The filtrate is then titrated potentiometrically to a pH of 7.6 using a 0.02 M NaOH solution to get the results for the acidity.

Aluminum in 1 M KCl extract - determination by ICP-OES

Aluminum ions are extracted from the soil sample with 1 M KCl solution and the soil is filtered from the extracts. The filtrate is used for pH determination and determination of aluminum content by ICP-OES.

Acidity of 1 M NH₄OAc extract (pH = 7.0)

The sample is extracted with 1 M NH₄OAc solution. The filtrate is titrated potentiometrically to a pH of 7.0 using a 0.1 M NaOH solution to get the results for the acidity.

Base cations in 1 M NH₄OAc extract (pH = 7.0) - determination by ICP-OES

The sample is extracted with 1 M NH₄OAc solution. After filtration, the concentration of Ca, K, Mg, Mn and Na is determined by ICP-OES.

Orthophosphate

Orthophosphate reacts with molybdate and ascorbic acid to form a blue compound that is measured at a wavelength of 660 nm photometrically by continuous flow analysis.

Ammonium, nitrate and nitrite

The soil sample is frozen and extracted in 2 M KCl. The concentration of NH₄-N and NO₃-N in the extract solution is determined photometrically by continuous flow analysis. When analysing nitrate nitrogen (NO₃-N), the sum of nitrate plus nitrite nitrogen is obtained.

Electrical conductivity - determination

The soil sample is extracted in water to dissolve the electrolytes. After filtration, the electrical conductivity of the filtrate is measured.

Extractable plant nutrients - extraction with CaCl₂-solution - determination by ICP-OES or CFA

The soil sample is extracted with 0.01 M CaCl₂ solution. After filtration, the concentration of P, K, Ca and Mg is determined by ICP-OES. Alternatively, orthophosphate is determined photometrically by continuous flow analysis.

Extractable plant nutrients - extraction with ammonium lactate-acetic acid solution - determination by ICP-OES

The soil sample is extracted with ammonium lactate/acetic acid solution. After filtration, the concentration of P, K, Ca, Mg and Na is determined by ICP-OES.

Extractable plant nutrients - extraction with HCl-solution - determination by ICP-OES

The soil sample is extracted with 2 M HCl. After filtration, the concentration of P, K, Ca, Mg and Na is determined by ICP-OES.

Extractable plant nutrients - digestion with HNO₃-solution - determination by ICP-OES

Soil or plant samples are digested with concentrated nitric acid. After filtration the concentration of P, K, Ca, Mg, Na, Cu, Zn, S, Fe and Al is determined by ICP-OES.

Elements in oxalic acid ammonium oxalate extracts (pH = 3,0) - determination by ICP-OES

The soil sample is extracted with 0.2 M ammonium oxalate/oxalic acid. After filtration, the concentration of P, Al and Fe is determined by ICP-OES.

Elements in extracts with 0.5 M NaHCO₃ (Olsen method) - determination by ICP-OES

The soil sample is extracted with 0.5 M NaHCO₃ at pH 8.5. After filtration, the concentration of P is determined by ICP-OES.

Phosphorus sorption index (PSI) - determination by ICP-OES or CFA

The soil sample is shaken with phosphorus-containing solution. After filtration, the phosphorus content of the supernatant is determined, and the degree of sorption is calculated. The concentration of phosphorus is determined by ICP-OES, alternatively the concentration of orthophosphate is determined by continuous flow analysis.

Greenhouse gases, methane and nitrous oxide - determination by headspace gas chromatography, HS-GC (FID/ECD)

The sample is collected in a vial by the chamber method. The sample is separated as it flows through a separation column for permanent gases. Methane is detected and quantified using a flame ionisation detector. Nitrous oxide is measured using an electron capture detector.

Analysis of cereals, legumes, and oilseeds using Near Infrared Transmittance (NIT)

NIT analysis determines quality parameters such as protein, water content, starch, and oil. The samples need no milling step but need to be clean before analysis. The system is based on spectroscopic measurement. The spectrum obtained is used in mathematical calculations to predict various parameters such as protein, water content, starch, and oil.

 The analysis can be performed on wheat, oats, rye, barley, field beans, peas, and rapeseed. Depending on crop type different parameters are of interest and can be analysed.