What is the effect of temperature on mineral content & pH in alfisols?

My interest in the effects of fire on ecosystems was piqued by the recent spate of devastating bush fires in Australia. In the bush, fires frequently occur as part of the ecosystem. Minerals from the burned vegetation are restored to the soil with the ash. What about the organic material in the soil itself, though? Does that burn as well, or is it only the vegetation? In wildfires, temperatures can reach over 250°C at the soil's surface and as high as 114°C in the top 2.5 cm of the ground. But at 7.5 cm, the temperature drops to 59–67°C. What impact would this have on the soil's mineral properties? I made the decision to look into how heating local soil samples within this temperature range affected the pH and a few minerals for which there were appropriate testing.

What impact does temperature have on the chemical properties of pH and the mineral properties of phosphorus, nitrogen, and potassium content of alfisol soil (70, 80, 90, 100, and 110°C)?

The increased temperature will cause microorganisms and organic matter to burn, increasing the amount of minerals in the burned soil. These microbes and organic matter control the bio-geochemicals of minerals like phosphate, nitrate, and potassium in soil for absorption by plants. The same organic matter burning will make the burned soil more acidic.

Background investigation: Alifisols are soils that have had part of their minerals washed away. Despite their frequent lack of phosphate and nitrogen in Australia, they have a reasonably high reproductive rate. These soils primarily developed beneath hardwood forests and have a clay subsurface.

Proteins, vitamins, and chlorophyll contain nitrogen. Nitrate (N0₃^-), which comes from the mineralization of organic materials and the use of fertilisers, is absorbed by plants and is necessary for the growth of vegetative activity. Additionally, water nitrates irrigate the soil. Nitrogen single test by Hanna Technology.

In natural waterways, phosphorus is present as phosphate (P0₄ ^3-) ions. Waterways and irrigation systems from dams are to blame for the introduction of phosphate into the soil. By way of runoff pollution from industry, phosphorus may be accessible to soil. As a plant, phosphorus plays a critical role in the development of roots and buds. (Hanna Technology - Analysis of phosphate and phosphorus in water) However, eutrophication, or the abnormal and excessive growth of plants, is mostly caused by an overabundance of phosphorus.

Potassium is present in tissues responsible for the growth of plants (primary and secondary meristems) (Hanna Technology - Potassium in Agricultural examination). Potassium regulates how much water is absorbed by the roots and in the control of cellular activity. Potassium helps safeguard plants to diseases. The problem of lack of potassium is frequent in alfisol soils.

Complex carbohydrates are produced by soil-dwelling microorganisms and are utilised by plants as a source of energy. For plant absorption, plant enzymes break down big nutrient molecules like fulvic and humic acids into smaller ones. Mycorrhizae, a helpful fungus in the soil, function as a significant secondary root system and assist in delivering these synthesised materials to the plant roots. The ideal pH for these biological ingredients is 6.5 (according to Guide to Organics and Hydroponics in Gardening).

The control experiment, which is a part of the design, involves taking soil straight from the earth and testing it for pH, phosphate, nitrogen, and potassium without adding the independent variable of heat. By using this control, it will be possible to compare the normal soil composition with the subsequent mineral content after increased heat exposure.

Practical Risk Assessment and Safety The Risk Assessment strategy takes into account risk evaluation and practical safety measures. Please refer to the STUDENT ACTIVITY RISK ASSESSMENT and PRAC ORDER FORM in Appendix A.

The soil was taken from an uncontrolled woodland. The sample was taken in an area without any nearby agriculture in order to prevent any outside influences from changing the mineral content. It was also taken from the top 20 cm of the soil, at least 20 metres away from the track that provided access to the site. There was no recent history of fires at the location.

• Set the industrial oven to an experimental temperature of 110 degrees Celsius (or 100, 90, 80, or 70°C) in the practical setup room.
• Transfer the calculated soil mass to each crucible and record any qualitative findings.
• Place the crucible in the oven only when it has heated to the proper temperature.
• Permit the earth to burn for 24 hours.
• Take the crucible out and write down any qualitative findings (such as porosity and granularity).

For each method, five soil samples were heated. As a control, three samples were left unheated.

• Sample 4g of soil, place it in the proper test tube from the agriculture test kit, and then top off with distilled water to the lower graduation mark (2.5mL).
• Fill the test tube from the test kit with the contents of the packet marked "HI 3895-pH reagent," which includes barium sulphate and calcium chloride dehydrate.
• Put the test tube cap back on and give it a gentle shake for 30 seconds. Use the stopwatch to measure time precisely.
• To assure the creation of the colour complex, give the sample in the test tube 5 minutes to stand.
• Compare the sample colour to the pH color-card. the pH of the sample. For the best measurement, make sure the amount of light coming into the lab is maximised. Hold the colour card about 2 cm from the sample for comparison against a uniform white background.

• Add 120g of the soil sample to the beaker after zeroing the balance.
•  Apply a 120:960 reduction of the soil-to-distilled-water ratio (225:1800).
• To achieve optimal efficiency, give soil 24 hours to separate into its component parts, such as organic matter, clay, silt, etc. separation left undisturbed (the better the results of the mineral test, the clearer the extract gets)
• Transfer 2.5 mL of clear general soil extract to a test tube using a pipette. (avoid moving dirt, prevent stirring up sediment, and squeeze the pipette's bulb before dipping it into the solution used to extract soil)
• Add the contents of the test-specific reagents (potassium, phosphorus, and nitrogen; HI 3895-N, HI 3895-P).
• Put the test tube cap back on the device and tighten it. For 30 seconds, gently shake the test tube.
• Permit the sample to stand in the test tube for 30 seconds to allow the colour complex to develop.
• Using a uniformly white background and consistent lighting, compare the colour visible in the sample to the reference colour card.
• Note detailed observations and pertinent information.

To increase the amount of soil in each trial, rocks were taken out of the measured mass in crucibles. Mineral transport is not aided by rocks.

Some samples received additional Universal Indicator in order to demonstrate the pH of the soil.

In the tests, shaking the test tubes was necessary to get the reagents and soil extract to react roughly. As reagents may not have connected with soil in these shaken more softly compared to those shaken more forcefully, this may have led to inconsistent readings.

The graph displays the averaged findings from the experiment testing for the minerals potassium, nitrogen, and phosphorus. The graph shows the mineral content of the soil under different temperatures as well as the control (unheated). Although there doesn't seem to be a clear pattern for the other examined minerals, nitrogen and phosphorus, there does seem to be a trend towards rising potassium levels when the temperature rises above 90°C. It seems that 80°C and 90°C are the temperatures that create the maximum levels of phosphorus and nitrogen, respectively.

This graph compares the average pH values of the soil samples cooked to various degrees with the unheated control sample. Even while there is some difference between the unheated sample and the one heated to 70°C, there appears to be a general progressive reduction in pH values for the heated samples.

The graph displays the average findings from the experiment to measure the pH of burned soil. After the soil was subjected to rising temperatures, the pH level was measured and found to have decreased (becoming progressively acidic). The findings indicate that there is a relationship between rising temperature and soil acidity, with pH decreasing as temperature rises. This correlation is suggested by the linear trend line. The coefficient of determination (R² value), which is equal to 0.8929, supports this correlation. This score is high and suggests a negative correlation as well as a good match with the trend line.