Soil Organic Matter Determination

Soil Organic Matter Determination

Introduction:

There are various ways by which the soil organic matter content can be determined, one method which can be used is the use of loss on ignition method, and the other method is the laboratory method by Walkley and Black. The ignition method involves recording weight changes before and after heating the soil, however this method has various sources of errors which include the recording of ash weight after heating, the loss of soil structural water, the loss of carbon dioxide from other carbonates contained in the soil and the possibility of change of sulphides into sulphur dioxide. These are the major sources of error in this form of experiment. In this experiment we are going to consider the loss on ignition to determine the organic matter contained in soil.

Methods:

In order to undertake our experiment a number of soil samples from a selected area were collected, the sampling method used was random sampling where 3 samples were obtained, the three empty pylex beakers were weighed and values recorded, further each beaker was marked using heat resistant ink for identification purposes. The soil samples was then put into the three beakers and weight recorded for each sample, all the three sample were then placed in an oven at 400 degrees for eight hours, I preferred to use the oven which would be a substitute to the furnace.

After eight hours the soil samples were removed from the oven using tongs to avoid injury that would be caused by the already hot beakers, they were then weighed and the values for each sample recorded, using the collected data from the three samples the determination of organic matter loss was to be possible, the mean change in weight for the three samples was determined and further value calculation was made to determine the organic matter content of the soil.

Soil Organic Matter Determination

Results:

For one of the sample the empty beaker weight was 32.3 g, after soil was added the beaker weight was 42.01 g, therefore to determine the weight of the soil added this was determined by subtracting the beaker plus soil weight minus the empty beaker weight, the results were as follows:

42.01 g– 32.30g = 9.71g

After heating the beaker the weight was recorded and the value was 41.85g, to determine the weight loss which was to be the weight of the organic mater lost then we subtract the weight of beaker plus soil weight after heating from the beaker plus soil weight before heating, this is as follows:

42.01g – 41.85g = 0.16g

Therefore from the above calculation the weight of organic matter loss from heating was 0.16 g.

The percentage loss on ignition is calculated as follows:

Weight of soil and beaker before heating – weight of soil and beaker after heating

─────────────────────────────────────────────── X 100

Soil Organic Matter Determination

Weight of soil and beaker before heating

Therefore we substitute the values and the result will be as follows:

42.01g – 41.85g                                                      0.16g

────── ──   X 100     =            ───── X 100   = 0.380862 %

42.01g                                                                      42.01g

Therefore the percentage organic matter content is equal to 0.380862 %

Discussion:

From the above results it was evident that the organic matter percentage level was 0.38% meaning that there is a very low organic mater content in the soil, difficulties would have been faced due to the structural soil water and also the conversion of sulphides into sulphur dioxide, further problems were faced in the organization where an oven was used in the experiment instead of a furnace as specified in the manual.

Soil Organic Matter Determination

Soil is classified depending on the size of particles and also the level of organic matter it contains, the loamy sand soils will usually contain less than 1% of organic matter, silt loam will contain 1 to 4% of organic matter and therefore it is clear that due to the lwo level of organic matter in this soil we can conclude that because it contain less than 1% of organic matter then the soil type is loamy sand.

References:

Brady N. (1984) The nature and properties of soils, Macmillan publishers, New York

Rowell D. (1994) Soil science: methods and applications, Longman press, UK

White R. (2006) Principles and practice of soil science, Blackwell publishers, Oxford