Effects Of Different Treatments On Soil Microflora Biology Essay


Microflora in soils refers to any of the bacteria, Actinomycetes, Fungi, Algae and viruses occupying the niche in the soil environment. Soil microflora fundamentally is governed by the type of soil, temperature, moisture, plant growth, nutrients, pH, and many other aspects which may vary between places to place and also within a single plot and over very small distances ( Davidson et.al 2000).

According to Schlesinger and Andrews (2000) soil microbial biomass comprises less than 5% of organic matter in soil nevertheless it executes at least 3 critical functions in soil and the environment. It is a labile source of carbon, nitrogen, phosphorus, and sulfur; it is an instantaneous sink of carbon, nitrogen, phosphorus and sulfur; and it is an agent of nutrient transformation and pesticide degradation. On top of that microorganisms form a symbiotic association with roots, act as biological agents against plant pathogens, contribute towards soil aggregation, and participate in soil formation.

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Schlesinger and Andrews (2000) continues by stating that soil microflora response to the environment can be measured by measuring the total respiration of the population using the soil incubated in jars with carbon dioxide traps. This mechanism is based on the fact that all soil microorganisms respire and during respiration there are changes in the concentration of CO2. When soil is incorporated with some compound, soil microflora respond by either using it as a substrate or if toxic may die from it hence they will leave it alone. The responses often result in an increase in the soil population if the compound is used as a substrate or a decline if the compound is toxic. These changes are often reflected by the increase or decrease in soil respiration. The higher the soil microbial population, the higher the amount of CO2 released .

According to Chang et.al (2007) when glucose is incorporation into soil, rapid evolution of CO2 occurs and is accompanied by a similar increase in bacterial numbers. The amendment is used primarily by bacteria and was wholly expended within the first 2 days of incubation. Subsequently fungal growth will be noted at the time the bacterial count declines. The developing bacterial population will follow the typical sigmoid growth curve and a minimum generation time of 2 hours will be obtained during the period of 5 to 10 hours after adding the glucose.

Pesticides are the chemical substances that kill pests. In the case of soil, pests are fungi, bacteria insects, worms, and nematodes etc. that cause damage to field crops. Thus, in broad sense pesticides are insecticides, fungicides, bactericides, herbicides and nematicides that are used to control or inhibit plant diseases and insect pests (Zhou et.al 2002).

Hypothesis: H0- Different treatments on soil have no effect on soil microflora

H1- Different treatments on soil have an effect on soil microflora

The purpose of this study was to find out the effects of different treatments on soil microflora as estimated by soil respiration.



200g of fresh soil was weighed into a 2L mason jar and enough water added to bring the soil to a 60% moisture holding capacity. A corresponding treatment to the soil was added to the jar and mixed well. A burette was used to measure 25ml of NaOH into the small beaker and placed into the mason jar. Tap water of approximately 5ml was placed into the test tube and placed inside the mason jar to maintain humidity. The jars were sealed tightly and incubated in the cupboard at a room temperature. A blank jar which only contained NaOH and a test tube of water was prepared

Determination of the amount of CO2 evolved

NaOH beaker was removed from the jar after a week. Several drop of BaCl2 were added to precipitate the excess carbon dioxide as BaCO3. Few drops of phenolphthalein indicator was added. The unneutralized alkali was titrated with 0.5N HCl using a burette until the end point was reached, colour change from pink to clear milky white. The beaker was washed then a fresh 25ml of 0.5N HCl was measured and incubated until the next lab session. The CO2 evolved during the week was calculated using the following formula: milligrams C or CO2 = ( B-V)NE where V= volume (ml) of acid used to titrate sample in the NaOH collectors B= Volume(ml) used to calculate the Blank N= normality of acid E= equivalent weight. If data is expressed in terms of carbon E= 6; if expressed as CO2 E= 22

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Setup of the in situ observation experiment incubation of Rossy cholodyney slides , titration and reincubation

NaOH traps were removed from the jars incubated on the last lab session and titrated with HCl using the same procedure as before. Rossy cholodyney slides were prepared and incubated in the soil in the jars as it was demonstrated. The beaker from the first step was washed and then 25ml of fresh 0.5N NaOH was measured then reincubated till the next lab practical.

Removal and heat fixing of Rossy Cholodney slides

NaOH traps were removed from the jars incubated on the last lab session and titrated with HCl using the same procedure as before. The beaker from the first step was washed and then 25ml of fresh 0.5N NaOH was measured then reincubated till the next lab practical. Following the demonstration and instructions outlined in the Rossy cholodney handout, the buried slides were gently removed. The slides were heat fixed and stained with crystal violet and methylene blue. The slides were air dried and kept for microscopic observation on the following week.

Final titration, Microscopic Observation of the buried slides

NaOH traps were removed and titrated with HCL then the glass wares were washed up. All the soil were placed in one plastic bag and handed back for disposal. The effect of different treatments on the in situ microbial population was observed using the light microscope.


Fig 1: shows a histogram of CO2 produced under different soil treatments in four weeks

Trend: Soil treated with glucose, sawdust, chicken manure, oil, pesticides, and Chicken manure shows a decrease in the amount of CO2 produced as the weeks progressed while in untreated soil and paper there was some fluctuation in the amount of CO2 produced in each week

Fig 2: average of CO2 on different soil treatment

Trend: Soil treated with glucose have the highest CO2 produced followed by chicken manure, paper sawdust, oil, NH4NO3, untreated soil, pesticides and blank respectively


Soil treated with oil

Soil treated with glucose


Soil treated with sawdust

Soil treated with chicken manure

Soil treated with pesticides

Soil treated with NH4NO3

Soil treated with paper

Fig 3: diagrams of microbials obtained in situ

Table 1: An Anova table for the result

Source of Variation






F crit

Between Groups







Within Groups












Figure 2 shows that the soil which have been treated with glucose have the highest carbon dioxide followed by the soil which were treated with chicken manure, paper, oil, NH4NO3, untreated soil and pesticides respectively. Based on the literature review from Schlesinger and Andrews (200) high amount of CO2 implies that the soil respiration is high since CO2 is a product of respiration. Glucose, Chicken manure, and paper have a lower carbon to nitrogen ratio hence it is easy for the microorganisms to degrade them by the process of respiration. Oil and NH4NO3 require a high carbon to nitrogen ratio and hence it is difficult for them to be degraded, on top of that NH4 is toxic to microorganisms therefore it will reduce the microbial population reducing the amount of soil respiration and this also implies to the pesticides.

In fig 1 the gradual decrease in the amount of carbon dioxide produced per week might have resulted due to the reduction of nutrients in the soil and that fluctuations in the amount of CO2 produced between the weeks on the same treatment might be due to the fact that when introducing different treatments, microorganisms take them as foreign substances and hence they take time to adopt to them.

If we take a family-wise α = 0.05. Our P-value obtained from table 1 is 9.7109 which is above our family- wise α of 0.05 hence we fail to reject the null hypothesis and conclude that there is no significant between the treatments or groups.