- Soil moisture
- Chlorophyll a
- Inorganic nitrogen
- Ammonium and nitrate
- Total N, total C, organic and inorganic C
- Electrical conductivity
Gravimetric Soil Moisture
Use analytical balance with precision to 0.1 mg.
- Pre-weigh aluminum weighing dish.
- Without taring dish, add field moist soil and weigh.
- Place into drying oven at 105°C for 24 hours.
- Remove oven-dry soil and place in desiccator to cool down. Weigh.
- Calculate soil moisture:
A. Sampling and extraction
- Sample from top 5 mm of soil only.
- All procedures are carried out in the dark to prevent degradation of chlorophyll.
- Mix thoroughly and place 10 g soil in a 20 ml screw cap vial.
- Add 10 ml of 90% acetone to each vial and swirl once gently.
- Place vials in 5°C incubator overnight.
- Adjust solution to pH 9.0. The solution must be basic because acidic chlorophyll contains pheophytin which will interfere with the spectrophotometric analysis of the chlorophyll.
- Filter solution through a Whatman GF/C filter and place in a screwcap test tube. Keep refrigerated.
B. Determination of Chlorophyll a concentration
- This procedure is carried out using a spectrophotometer.
- Blank the spec with a 90% acetone solution.
- Place 3 ml of extracted solution in a cuvette. Measure the absorbance at 664 nm and 750 nm. This must be done fairly quickly in order to prevent light from breaking down the chlorophyll.
- After taking the initial measurements, add 0.1 ml of 1N HCl directly to the cuvette and agitate gently. Wait 90 seconds, then re-measure the absorbance at 665 nm and 750 nm. The acid will convert the chlorophyll to pheophytin by releasing a magnesium ion in an acidic environment.
- Use the following equations to calculate the concentration of chlorophyll in your soil sample:
chlorophyll a (mg/m3) =
- V1 = volume of extract in liters
- V2 = volume of soil sample in m3
- L = light path length of width of cuvette, in cm
- 664b= optical density of 90% acetone extract before acidification
- = (absorbance at 664 nm) – (absorbance at 750 nm)
- 665a = optical density of 90% acetone extract after acidification
- = (absorbance at 665 nm) – (absorbance at 750 nm)
- Standard Methods for the examination of Water and Wastewater, Vol. 18, pages 10-18 to 10-19
- The seasonal periodicity of algae on Antarctic fellfield soils. Holarctic Ecology 14: 112-120. 1991
- Chlorophyll a determination of periphyton on sediments: identification of problems and recommendation of method. Freshwater Biology 20: 347-352. 1988.
- A note on the extraction of chlorophyll from benthic algae using methanol. Aech. Hydrobiol. Beih. Ergebn. Limnol. 14: 88-90. 1980
KCl Extraction for Inorganic Nitrogen (Keeney and Nelson, 1982)
- Weigh out 8 g air-dried, 2 mm sieved soil into a 125 ml Erlenmeyer flask.
- Dispense 40 ml of 2M KCl into each Erlenmeyer flask including blanks.
- Cover Erlenmeyer flasks with parafilm and place on a shaker. Shake for 1 hr on low speed setting.
- Pour liquid through Whatman #40 filter paper.
NH4+ and NO3- determination
Ammonium and nitrate concentrations were determined using a Flow-Injection Autoanalyzer made by Lachat Instruments (Milwaukee, Wisconsin), model Quikchem AE System. [Lachat is now Zellweger Analytics, Inc., Lachat Instruments Division.] The instrument analyzes for NO3–N and NH4+-N colorimetrically as mg l-1 in KCl solution. The final results are presented as mg kg-1, where mg is NO3–N or NH4+-N and kg is soil mass.
Keeney, D.R. and D.W. Nelson. 1982. Nitrogen-Inorganic forms. In : A.L. Page (ed.). Methods of soil analysis. Chemical and microbiological properties. Agronomy 9 (2): 643-698. Am. Soc. of Agron., Madison, WI.
Total nitrogen, Total carbon, Organic carbon, Inorganic carbon
These parameters were analyzed using an elemental analyzer made by Carlo Erba Instruments (Milan, Italy). The instrument uses a combustion method converting all forms of N or C into N2 and CO2 gases. The N2 and CO2 gases are separated by gas chromatography and analyzed by a thermal conductivity detector. The final results were presented as unit mass of N or C in soil per unit mass of soil, expressed as g kg-1
Soil samples were dried and ground prior to analysis for total N and total C determination. For organic C determination, soil samples were pretreated with HCl to remove carbonate and bicarbonate, the major components of inorganic C. Inorganic C was determined by subtracting the organic C from the total C.
These measurements were made in a 1:2 water suspension: one part of soil in two parts of deionized water without filtration. We used a Hach One Laboratory pH Meter and Model 44200 Combination Electrode (Hach Company, Loveland, Colorado). The measurements were taken at 22°C.
These measurements were made in a 1:5 water suspension: one part of soil in five parts of deionized water. The solution was centrifuged at 1000 g for 10 minutes to settle out particulates. We used an Orion Model 160 Conductivity Meter and Model 016010 4-Electrode Conductivity Cell (Orion Research Incorporated, Boston, Massachusetts). The measurements were recorded as dS m-1. All readings were adjusted to 25°C.