Introduction:
In this experiment, we retrieved five different soil samples and measured 5 different parameters cation exchange capacity, soil texture, nitrate-N, soil pH, and electrical conductivity to analyze their makeup. Our goal was primarily to understand and identify if there was a correlation between cation exchange capacity and soil texture, nitrate-N, soil pH, and electrical conductivity. Such that our null hypothesis for this experiment is there is no correlation between cation exchange capacity to the other four parameters (soil texture, Nitrate-N, soil pH, electrical conductivity). However, more general goal were trying to be met in this experiment such as seeing what influences soils, in general, by using unique locations by looking at all the five different parameters indicated. We aimed to understand how different aspects of a soil can change these parameters. Even further this experiment another goal was to learn how to analyze different soils and draw conclusions about why it is that way and how it became to be that way. We aimed to understand the different aspects that make up the soil quality and how that affects it function in that particular piece of land even if it is not for biological productivity.
Texture shows the content of particles of various sizes (i.e. sand, silt and clay) in a soil sample, it influences how workable a soil is and how much water and air it holds, and the how fast or slow he water can flow through. What can influence the texture include the parent material (1) which soils will “inherit” and the properties of its parent material like color, texture, and composition influence the texture. Another is inorganic materials (2) (i.e. sand, clay, silt), the different sized particles that make up the soil are the inorganic materials and give the soil its texture, and the amount of inorganic materials in soils are different, which affects the texture of soils. Inorganic particle sizes (3) also affect the soil sand particles have the largest size (0.05 – 2.0 mm in diameter), silt particles are smaller (0.002 – 0.05 mm in diameter), and clay is the smallest (less than 0.002 mm in diameter) and that affects the texture by changing how air and water can enter and stay in the soil. Climate (4) influences soil texture greatly by having energy and precipitation influencing physical and chemical reactions on parent material, and it determines vegetation which influences soil development.
Cation exchange capacity (CEC) is a measure of how many cations can stay on soil particle surfaces. A factor that influences CEC is soil texture (1), and it is based on how the type of soil can attract and hold the positive ions; for example, clay attracts positively charged cations and holds them and CEC of soils increases with increase as clay content does while soils with a lot of sand keep smaller amounts of cations; the finer the texture the more CEC and each mineral has it own CEC and the more clay present the more CEC. Soil organic matter (2) also plays a role in CEC when there is a lot of organic matter, it increases CEC. What influence the organic matter is the pH of the soil (3) and the greater pH creates a sweeter soil, which influences the plants which in turn makes CEC increase and influence the soil. Another factor is the nature of clay minerals (4) , smectite has the greatest, next fine mica, least is kaolinite. CEC of a soil is influenced by those minerals in the soil (5) since they exchange the retention of cations. Finally soil reaction (6) effects the CEC, as the pH increases, the hydrogen held by kaolinite becomes ionized and replaceable, so the result is that the negative charge on the colloids an increase nd influence on the CEC.
Nitrate-N is the concentration of nitrates and is the nitrogen present. The rainfall (1) and temperature (2) can affect nitrate-N as it affects moisture, aeration, and salt which can raise or lower N, so they influence the rate of N mineralization from any from organic decomposition, nitrogen cycling, and nitrogen loss (i.e. leaching, runoff). How the soil is tended (3) to affects the Nitrate-N because aerated soils can release N easier and faster compared to saturated soils which trap the N in. The amount of organic matter decomposition (4) affects this too as more N is released when plants/organic materials break down and this happens more quickly in warm, moist climates and more slowly in cool arid climates, so temperature (2) affects this as mentioned above. Soil texture (5) plays a role in Nitrate-N as leaching is dependent on the soil’s percentage of sand, silt and clay and its water content. Water can flow easier in the large spaces (sand) than in smaller pores (clay), so it is harder to hold water in sandy soils than clay soils. Soils that have poor drainage because of the pores can be saturated which causes denitrification resulting in a loss of N affecting the measurement.
Soil pH measures the acidity or basicity of a soil. A factor affecting the soil pH could be temperature (1) and humidity (2) for example in warm, humid environments the soil pH decreases due to soil acidification, due to leaching from a lot of rainfall and In dry climates soil weathering and leaching are less intense and pH can be neutral or alkaline. Soil texture (3) affect pH, soils with high clay and organic material resist a decrease or increase in pH (greater buffering capacity) than sandier soils. Parent Material (4) can also affect the pH uniquely as soils formed from sandstone or shale are more acidic than soils formed from limestone. Flooding (5) in the area can affect the pH since the pH will approach neutrality during flooding changing the original acidity or basicity of a soil.
Electrical conductivity is the indirect measurement that correlates to soil physical and chemical properties, it is the ability of a material to conduct an electrical current. Weather (1) can affect EC as in arid, dry areas salts are more likely to accumulate and stay under the soil surface, resulting in high EC. The type of land (2) affects the EC so low altitude areas where water can accumulate have higher EC than areas of high ground because water travels into soils can interact with the underlying material that then weathers, releasing salts changing the EC. Soil texture (3) can affect EC as soils that have more smaller soil particles AKA clay can conduct more electrical current than soils that have larger silt and sand particles. A factor that could affect EC could be electrolytes that live in the groundwater (4) as that can increase the conductivity of the soil
Methods:
When collecting the unique soil types, samples from different areas were chosen throughout our Neighborhood in the general Central park area in late fall. Soil samples that were chosen were chosen because of the following and to be noted we took soil just from the top layer as we could not reach far down into the ground: soil from land that was unkempt and not regularly cared for (The Field), soil from land that was fertilized and extremely cared for (The Meadow), soil from land that should be acidic (due to the decomposition of pine needles) (Pine Trees), soil from a wet area (The Pond). The next was chosen without regard for the type of soil, rather it was a random sample. Originally, this sample was meant to be from soil inhabited by ivy which is often an invasive plant that suck nutrients out of its host extremely (especially English Ivy), this sample was not taken due to rules in the Central Park Conservatory regarding taking their soil. Instead, a sample from an area that had shrubbery was taken. We took a shovel and a ziplock bag (and a backpack to carry it in to be discrete) to collect the samples. In one collection, one collection per day that we were able to go out, 4-6 shovels of dirt were put in the bag, and it samples should be taken from different areas in the chosen location, not all from the same spot, to be taken back to be processed for the individual lab methods regarded below. While part of the group are in the lab doing and preparing to follow the procedure, the other part will go out and collect the samples to then come back and set the dirt out on parchment paper to dry overnight, or for us our next class period.
Refer to Soil Methods PDF for the general procedure of this experiment. However, there were some changes made regarding the procedure. In the section that gives the method to determine Cation Exchange Capacity we washed generally washed the soil once (we considered that the clay portion of the soil clogged the pores) that would allow the because our vacuum was not strong enough to bring the ammonium acetate and 70% isopropanol quickly through the filter paper. Instead the liquid soaked the soil sample and slowly dripped through which assured that our sample was washed.
Results:
Discussion:
There are not extremely high correlations in any of the graph, however the strongest correlation was the CEC compared to the pH. The greatest factor of limitation is that lab procedures took procedure on the days in which we had class so the soil could be sitting out and being to denitrify and break down in the span of 24 hours to even 3 days. There was not a continuous time frame for the experiment, it stopped and started. Also our sampling was very small, only 4-6 shovelings so it can not possibly represent the entire location whether a field or a pond, so it is a very limited sampling so it can not describe a location completely. Another limitation is that the experiment took place at a certain time of year, season changes change primarily precipitation and temperature so anything from soil moisture (i.e. snow in winter, rain in the spring), evaporation rates, and organic matter decomposition (i.e. leaves falling in autumn, plants dying in winter) all of which would affect the 5 parameters we measured for. We found only 2 apparent correlations between the parameters when analyzing our soils. From this experiment’s results the null hypothesis was correct for CEC compared to Nitrate-N and EC, but it was incorrect regarding pH and soil texture/percent clay as it generally correlated, following the line of best fit. We found what specifically can influence the CEC in each of our chosen locations with the different parameters. More importantly in this experiment we looked at the difference in soil quality and how completely different location’s soil profiles are that way for a particular reason (i.e. acidity from decomposing pine needles, pine trees grow best in clay soils).
Although the R2 value for the clay % vs. the CEC did not indicate strong correlation, as it was less than the other 2 graph which we undoubtedly uncorrelated, the graph indicates a slight correlation. Looking at the graph, the third data point looks as if it is an outlier which can decrease the correlatibility of the graph as a whole. Without thi point the R2 value is .5141, which us a moderate negative correlation. Clay rich soil is slow-draining and relatively dense so not many trees can thrive ideally in this kind of soil, but there are a few like pines and other evergreens because of the water retaining well and being nutrient-rich soil. This outlying point was one from the location that had pine trees in it. Soils that primarily clay and organic matter tend to have a higher CEC, that is because the clay mineral and organic matter in the soils are negatively charged locations that will hold the positively charged ions by electrostatic attraction. In comparison of these 2 parameters there was supposed to be a positive correlation since CEC increases when clay % increases, a possible reason for this result could be because of the pond data point since it has a high CEC but a low clay content. Organic matter significantly influences because of its makeup so it is CEC is highest at the surface. The high CEC could be due to high organic matter in our sample that throws off creating a concrete correlation and understanding the relationship between clay % and CEC. High CECs mean a higher percentage of clay makes up the soil which means more water can be held than sand and silt soils. Negative clay particles have a larger surface area so can hold more water and nutrients so it would have a higher CEC since it has high retention (which is key for fertile soil).
The CEC and pH have a positive correlation, and the R2 value is .4072, which means that it has correlation overall. When it is square rooted the correlation constant is .63 which means it has a relatively higher correlation since CEC increases with pH which matches our positive correlation. There is an outlier in this graph which was point three, point three was the location that had a more acidic pH when compared to the CEC this was because it was the pine tree location. Pine needles have a pH of 3.2 to 3.8, which means it is acidic so when the pine needles fall and decompose when left of the topsoil/ground surface they will slowly make the soil pH more acidic. When a soil is more acidic the H+ cations the absence of negatively charged locations in the soil makes it difficult for the cations to stick to the soil making it less fertile, so the CEC is greater when the soil is more basic. The other points follow this trend making the correlation. Soils with a low CEC, more acidic soils, are likely to develop deficiencies in cations key to make a fertile soul while high CEC soils are resistant to losing cations due to bonding.
References:
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Factors Affecting Cation Exchange Capacity Environmental Sciences Essay. (n.d.). Retrieved
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Factors that influence soil pH. (n.d.). Retrieved November 8, 2018, from
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