The Soil and Plant Laboratory

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

Determination of 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.

Total carbon and nitrogen - determination by LECO

The sample is burned at 1350°C in pure oxygen, after which the combustion gases are analyzed for carbon dioxide and nitrogen. The result is given as percentage by weight of carbon and nitrogen. For the determination of organic carbon, the samples are first annealed at 550°C and analyzed, then the remaining carbonate carbon is burned at 1350°C. The organic carbon content is then calculated. The organic carbon content is then calculated as: Org-C = Tot-C - Carb-C.

pH of water extract

The soil sample is mixed with water to form a suspension. pH is measured on the suspension.

In the EN ISO 10390:2022 method and the 'House method' the suspension is mixed in a volume:volume proportion, while in the MI method the suspension is mixed in a mass:volume proportion (1:5 in all cases).

pH of 0,01 M CaCl2 extract

The soil sample is mixed with 0,01 M CaCl2 solution to form a suspension. pH is measured on the suspension.

In the EN ISO 10390:2022 method, the suspension is mixed in volume:volume proportion, while in the MI method the suspension is mixed in mass:volume proportion (1:5 in both cases).

pH of 1 M KCl extract

The soil sample is mixed with 1 M KCl solution and the soil is filtered from the extracts. The filtrate is used for pH determination.

Acidity of 1 M KCl extract

The sample is extracted with 1 M KCl solution. After filtration, a potentiometric titration to pH 7,6 is carried out with 0,02 M NaOH and the acidity is obtained.

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. After filtration, a potentiometric titration to pH 7,0 is carried out with 0,1 M NaOH to obtain 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 - determination by autoanalyzer (Segmented Flow Analysis, SFA)

Orthophosphate reacts with molybdate and ascorbic acid to form a blue compound that is measured at a wavelength of 660 nm. The calibration range is 0.05 - 50 mg/L as P.

Ammonium, nitrate and nitrite by autoanalyser (FIA)

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 colorimetrically by autoanalyser. When analyzing 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 calcium chloride (CaCl2) - determination by ICP-OES or SFA

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 colorimetrically by segmented flow analysis, SFA (Autoanalyser).

Extractable plant nutrients - extraction with ammonium lactate-acetic acid solution (AL) - 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 hydrochloric acid (HCl) - 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 nitric acid (HNO3) - 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 ,Al and B 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 SFA

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 segmented flow analysis, SFA (Autoanalyser).

Greenhouse gases, methane and nitrous oxide - determination by headspace gas chromatography, HS-GC

The sample is taken in a vial by the chamber method. The sample is separated as it flows through a permanent gas separation column. Methane is detected and quantified using a flame ionization detector. Nitrous oxide is detected using an electron capture detector.