Soil Analytical Tests

NH4-N.

This is a soil fertility test. This method involves the extraction of ammonium (NH4 -N) from soils using 2.0 N KCl. Ammonium is determined by spectrophotometric, diffusion-conductivity instruments or distillation techniques. The method doesn't quantitatively extract ammonium from mineral structures (i.e. nonexchangeable NH4 -N) or bound to organic compounds. Soil ammonium concentrations are generally low in mineral soils (< 10 mg kg-1). The method detection limit is approximately 0.2 mg/kg and is generally reproducible ± 7%.

HCO3.

This is a soil salinity test. This procedure quantifies bicarbonate (HCO3 1-) concentration in mmolc L-1 in a soil saturation paste. The concentration of bicarbonate affects the solubility of calcium, the ionic strength of the extract solution and is used to calculate the adjusted sodiuim adsorption ratio. The method detection limit is approximately 0.05 mmolc/L and is generally reproducible within ± 10%.

BD.

Bulk density is the relationship of mass and volume of the soil. It is determined by drying the soil and determining the dried mass. The mass is then divided by soil volume.

CaCO3.

This method is determined by the loss of carbonates, in the form of carbon dioxide, in excess hydrochloric acid. Calcium carbonate (lime) is measured to determine soil buffering capacity. This procedure estimates the free calcium carbonate in a sample. The method detection limit is approximately 0.2% CaCO3 equivalent.

This is a soil salinity test. Cation exchange capacity (CEC) is the measure of a soil to retain readily exchangeable cations which neutralize the negative charge of soils. This method involves saturation of the cation exchange sites with ammonium. This method maybe poorly suited to soils containing carbonates, vermiculite, gypsum and zeolite minerals. The method detection limit is approximately 1.0 cmol/kg and is generally reproducible within ± 10%.

Cu. This is soil composition test by acid digest. This procedure analyzes the concentration of copper by utilizing a nitric acid/hydrogen peroxide closed vessel microwave digestion. Determination is by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The approximate method detection limit is 1 mg/kg.

EC (in 1:2 soil:water).

This is a soil salinity test. This method quantifies the amount of dissolved salts by measurement of the electrical conductivity of a soil saturated paste extract. The relationship between electrical conductivity and soluble salts is approximate due to differences in equivalent weights, ion equivalent conductivities, and relative proportions of major solutes in the paste extracts. Salt tolerance crop data is generally expressed in terms of the electrical conductivity of the saturation paste extract and used to assess the potential of soluble soil salts which may limit crop productivity. The method detection limit is approximately 0.01 dS/m (mmhos/cm) and is generally reproducible within ± 7%.

x-Ca.

This is a soil fertility test. This method determines the concentration of exchangeable calcium in the soil saturation paste extract using atomic absorption spectrometry (AAS) or Inductively Coupled Plasma Emission Spectrometry (ICP-AES). The method detection limit is approximately 0.02 mmolc/L on a solution basis and it is generally reproducible within ± 7%.

x-Mg.

This is a soil fertility test. This method quantitatively determines the concentration of exchangeable Magnesium in the soil saturation paste extract using atomic absorption spectrometry (AAS) or Inductively Coupled Plasma Emission Spectrometry (ICP-AES). The method detection limit is approximately 0.02 mmolc/L on a solution basis and it is generally reproducible within ± 7%.

x-Na.

This is a soil fertility test. This method quantitatively determines the concentration of exchangeable Sodium in the soil saturation paste extract using atomic absorption spectrometry (AAS) or Inductively Coupled Plasma Emission Spectrometry (ICP-AES). The method detection limit is approximately 0.02 mmolc/L on a solution basis and it is generally reproducible within ± 7%.

Fe.

This is a soil fertility test. The DTPA micronutrient extraction method is an extraction for estimating the potential soil bioavailability Fe. Analyte concentrations are determined by atomic absorption spectrometry (AAS) or Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The method detection limit is approximately 0.1 mg kg-1 and is generally reproducible ± 15%.

NO3-N, Olsen-P (Bray-P for pH<6), x-K.

This is a combined soil fertility test. It test the amounts of nitrogen, phosphorus and potassium.

Mg.

This is a soil salinity test. This method determines the amount of soil plant available magnesium on the soil colloid exchange sites by displacement with ammonium acetate solution buffered to pH 7.0. Cation concentrations are determined using atomic emission (AES), absorption spectrometry (AAS) or ICP-AES instrumentation. The method detection limit is approximately of 25 mg/kg and is generally reproducible ± 7%.

Mn.

This is a soil fertility test. The DTPA manganese extraction method is for estimating the potential soil. Analyte concentrations are determined by atomic absorption spectrometry (AAS) or Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The method detection limit is approximately 0.1 mg/kg.

NO3-N. This is a soil fertility test. This method involves the extraction of nitrate from soils using 40 g (0.02 N) CaSO4 solution. Nitrate is determined by reaction with chromotropic acid to form an azochromophore (yellow dye) which is measured spectrophotometrically at 420 nm. Soil nitrate-nitrogen can be used to predict plant response to nitrogen fertilizers. The method detection limit is approximately 1.0 mg/kg and is generally reproducible ± 6%.