Urea Concentrations and Soil Bacteria Activity Internal Assessment

Urea Concentrations and Soil Bacteria Activity Internal Assessment

Personal engagement

Soil microorganisms play an important role in the decomposition of organic matter, fertilizing the soil, and cycling nutrients. I have always loved agriculture and eliminating food shortage in the world has been my dream. It is through improved agricultural technology that my dream will come true. Soil bacterial will play a pivotal role in ensuring that there are fewer plant diseases as well as higher yields.  For the soil bacteria to function optimally, they need a conducive environment, such as the availability of organic matter. Understanding how soil bacteria perform in the presence of different urea concentrations will help in determining the fertilizers that can lead to higher agricultural production. Therefore, the internal assessment on urea concentration and soil bacteria activity is related to my personal life.

Exploration

The Effect of Different Urea Concentration and Soil Ph on Soil Bacterial Activity

Research question

This internal assessment will be answering the question: How does urea concentration affect soil bacterial activity?

The dependent variable is the rate of soil bacteria activity that will be measured during the five trials using soil with varying urea concentration.  The independent variable is the level of urea concentration that will be changed at different steps of the experiment. The controlled variable will be the soil solution without urea that will be used to detect the difference after adding urea to the other solutions.

Variables

A wide range of urea concentrations was used as the independent variable. The aim of using varying concentrations was to evaluate the functionality of urease in the soil. The urea was added at  0.00g, 0.02g, 0.04g, 0.06g, and 0.08g.

The rate of soil bacterial activity was measured in five trials when urea is added to the soil. The process was repeated several times under different concentration of the area.

The soil solution without urea was used as the controlled variable because it shows changes in the rates of hydrolysis when the concentrations of urea change. Using the urease bacteria only in all trials was important to avoid invalidating the relationship between the soil bacteria activity (dependent variable) and the levels of urea concentration (independent variable).

Hypothesis

The level of urea concentration determines the rate of soil bacterial activity.

Introduction

The decomposition of organic matter is a complex process that requires the combined efforts of various organisms. Microorganisms play a significant role by producing and releasing various extracellular enzymes that are required in depolymerizing and mineralizing complex organic compounds into smaller molecules that can be assimilated (Wang et al., 10). Urea fertilizers have been commonly used to improve soil fertility. When urea fertilizers are applied in bands, it is not possible to have a uniform concentration of urea in the soil solution. At the edge of the bands, the concentration tends to be very low. At the center of each band, the concentration is very high. Since urea fertilizers are a major source of reactive nitrogen, understanding the hydrolysis process is very important (Fisher, Stephanie, and Bruce 6). The soil bacteria are the key driver of soil nitrogen cycling. Therefore, knowledge of how the microbial community responds to the addition of different concentrations of urea is essential.

The nitrogen fertilizer, in the form of urea, has the highest demand worldwide. The addition of urea fertilizers to the soil leads to increased production of cereals and several crops, which are essential in feeding the ever-expanding world population. When urea fertilizers are applied to the soil, the nitrification process takes place, leading to the production of ammonia, which is converted to nitrite (NO₂) and (NO₃^–) (Kandeler and  Gerber 69). When different concentrations of urea are added to the soil, the rate of hydrolysis also changes. It has been observed that some nitrogen fertilizers reduce heterotrophic respiration because of the effects of carbon cycling and soil acidification. Increased availability of nitrogen fertilizer in the soil may favour nitrogen-limited species that use carbon sources more efficiently. Adding moderate levels of nitrogen fertilizer will make nitrogen-limited species to be more productive. When higher concentrations are added, more toxicity may occur, leading to limited diversity. Different soil types react differently to the addition of urea.

This study used four soil types with different pH collected from different fields in the school.  The soils were amended with different concentrations of urea. The study hypothesized that, despite differences in soil pH, amending urea concentration would have a similar effect on the rate of hydrolysis across all soils. The results of this study provide insights into how soil bacteria respond to the urea amendment, which can help in determining the urea concentrations that could lead to the optimal performance of soil bacteria.

Methodology

Control of variables

All soil samples with different pH were collected in the school compound. The soil was a widespread ecosystem type that is likely to be covering more than 70% of the agricultural area in Australia (Siewe et al. 412). Distilled water (20 x 10ml) was added to each 10 g soil sample in a test tube to adjust its water holding capacity to 85%. The soil pH was measured following standard procedures (soil-water ratio of 1:2.5). The soils were exposed to different concentrations of urea ranging from 0.00g to o.08g and adjusted to pH values of 5.5, 6.5, 7.5, 8.5 and 9. These urea concentrations covered a range of soil chemical conditions that actually occur after the nitrogen fertilizer application is made. Lower concentration represented uniform application methods, while greater concentration represented potential within fertilizer bands or close to the urea granules.

Soil solution after adding 0.06g of urea

Soil solution after adding 0.08 g of urea

Soil after adding 0.02g of urea

Soil solution after adding 0.00 g of urea

To make sure that no aggregates in the soil solutions, stirring was carried out on the soil slurries. Five trials were conducted every day for the different urea concentrations in the solutions. The process was repeated for seven days to ensure the accuracy of the procedure (Zhang et al., 70). After the test tubes were filled with the urea concentration, they were covered and stored for two hours at 18⁰C, while continuous shaking was taking place. This was done to ensure that the solution mixed well.

Data collection

The change in pH for each soil solution in the different trials was recorded. This was important in determining the rate of hydrolysis caused by soil bacteria. The results for the five trials in every day were recorded to ensure that the method was reliable. The level of urea concentration added to each soil solution was recorded alongside the resulting change in pH in the five trials.

Table 1 below was used to record the rate of hydrolysis when the level of urea concentration was 0.00g. The five trials were recorded in 7 days to detect any changes in bacterial performance and ensure accuracy and validity of the data.

Ph at 0.0g

Table 1. 0.00 g of urea.

Table 2 below was used to record the rate of hydrolysis when the level of urea concentration was 0.02g. The five trials were recorded in 7 days to detect any changes in bacterial performance to ensure the reliability of the data.

Ph at 0.02g

Table 2: 0.02 g of urea

Table 3 below was used to record the rate of hydrolysis when the level of urea concentration was 0.04g. The five trials were recorded in 7 days to detect any changes in bacterial performance and ensure accuracy and validity of the data.

Ph at 0.04g

Table 3: 0.04g of urea

Table 4 below was used to record the rate of hydrolysis when the level of urea concentration was 0.06g. The five trials were recorded in 7 days to detect any changes in bacterial performance and ensure accuracy and validity of the data.

Ph at 0.06g

Table 4: 0.06 g of urea

Table 5 below was used to record the rate of hydrolysis when the level of urea concentration was 0.08g. The five trials were recorded in 7 days to detect any changes in bacterial performance and ensure accuracy and validity of the data.

Ph at 0.08g

Table 5: 0.08g of urea

Data analysis

The soil samples were analyzed for pH (2:1 water ratio) and the urea extractable. For the urea, the test tubes were shaken for one hour and filtered through filter papers. The extracts were analyzed to determine the pH level at each trial. The maximum differences in soil pH and NH4-N (ΔNH4-N) between the urea-treated and control soil samples during the monitoring stage were determined. R software was used to compare cumulativeNH₃-N that was used during the various trials and the rest of the monitoring period. The same procedure was used to compare soil  NH₃-N concentration and soil pH for the various trials for every day.

Average =

9.5+9.5+9.5+9.5+9.5  = 9.5

Uncertainty   =  = 0.0052

Graph 1. Soil with 0.00g of urea

The bacteria activity drops slightly before rewetting the soil. Upon rewetting the soil, the bacterial activity increased. The pH level started dropping on the third and fourth days. It slightly increased during the fifth day. The activity started levelling off during the sixth day.

Graph 2. Soil with 0.02g of urea

The bacteria activity slightly dropped before rewetting the soil. Upon rewetting the soil, the bacterial activity rapidly increased and reached the maximum within the first 24 hours. The activity slightly dropped on the fourth day, but it started to level off thereafter.

Graph 3. Soil with 0.06g of urea

The bacteria activity slightly dropped before rewetting the soil. Upon rewetting the soil, the bacterial activity rapidly increased and reached the maximum within the first 24 hours. The activity slightly dropped on the fourth day, but it started to level off thereafter.

Graph 3. Soil with 0.08g of urea

The bacteria activity slightly dropped before rewetting the soil. Upon rewetting the soil, the bacterial activity rapidly increased and reached the maximum within the first 24 hours. The activity slightly dropped on the fourth day, but it started to level off thereafter.

In conclusion, the level of urea concentration affects the rate of soil bacterial activity. Once the soils were rewetted, the soil bacteria activity increased rapidly, reached a maximum within one day, and then started slowing down to level off after about three days. The soil bacteria activity increased with urea concentration, reached a maximum level, and started to decrease with rising urea concentration. Describing the results required a kinetic model with enzymatic reactions, both having varying affinities of urea. There was a slight decline which was followed by a sharp increase. The pH increased from 6.5 to 9.5. Following the Michaelis-Menten Kinetics, the high-affinity reaction had a small contribution other than the cases of low concentrations of urea. The urea concentration at which both reactions had equal contributions to the overall soil bacteria activity ranged between o.o4g to 0.08g.

Evaluation

The process was well designed, and the sample could be used to represent the soils of different regions of Australia. This made it easy to analyze the data and generalize the findings. The data was accurately recorded, making it consistent and reliable.

The weaknesses of the study include the fact that it was difficult to access related secondary data to make a detailed conclusion (Burbank et al., 391). The study was also not comprehensive enough to explain complex issues about the relationship between urea concentration and soil bacteria activity.

Future studies should make use of the available secondary data as well as use various soil samples to ensure that the data is valid and more reliable.

Works Cited

Burbank, Malcolm B., et al. “Urease activity of ureolytic bacteria isolated from six soils in which calcite was precipitated by indigenous bacteria.” Geomicrobiology Journal 29.4 (2012): 389-395.

Fisher, Kristin A., Stephanie A. Yarwood, and Bruce R. James. “Soil urease activity and bacterial ureC gene copy numbers: effect of pH.” Geoderma 285 (2017): 1-8.

Kandeler, Ellen, and H. Gerber. “Short-term assay of soil urease activity using colorimetric determination of ammonium.” Biology and fertility of Soils 6.1 (1988): 68-72.

Siewe, Ruth M., et al. “Urea uptake and urease activity in Corynebacterium glutamicum.” Archives of microbiology 169.5 (1998): 411-416.

Wang, Y-J., et al. “The effect of enrichment media on the stimulation of native ureolytic bacteria in calcareous sand.” International Journal of Environmental Science and Technology (2019): 1-14.

Zhang, Jingjing, et al. “Synthesis, characterization, and the antifungal activity of chitosan derivatives containing urea groups.” International journal of biological macromolecules 109 (2018): 1061-1067.