Soil Sampling and Analysis - Lab Report Example

Name: Lab Instructor’s Name: Date: Experiment: Soil Sampling and Analysis Objective The main aim of this experiment was to sample soils and carry out laboratory analysis to determine their salinity, pH and nutrient composition. Introduction Soil sampling and testing is a very important tool used in the assessment of soil characteristics such as physical, chemical and mechanical properties. Before submitting a soil sample for analysis, the samples should well represent the field under the test. The major concern when making a decision on how to collect representative soil samples is soil variability. Identifying appropriate locations that will yield a representative sample can be difficult if one lacks the knowledge and skills of soil sampling, which can lead to sporadic results. Regular testing of soil provides a valuable information for monitoring soil nutrient levels, and other important soil characteristics such as salinity and pH (Rayment and Lyons). Different crops require different nutrients in varying proportions. Analysing soil samples to determine the nutrients present enables one to choose the types of crops to grow and the type of fertilizers to apply in order to meet crop nutrient requirements to boost crop yield. Salinity and soil acidity also plays a very significant role on crop nutrient requirements and yield potential of a crop field. The adverse effects of soil pH on crop growth as well as different adaptabilities to soil pH can influence nutrient uptake and crop yield (Landon). Soil salinity also affects growth of crops and yield potential by increasing the soil’s osmotic pressure. As the soil becomes excessively concentrated with salt, the crop growth rate and final production progressively decreases (Faithfull). In this experiment, three representative samples were collected within the campus and then analysed in the lab using simple techniques to determine the nutrient levels, soil acidity (pH) and salinity of the soil samples. Experimental Procedures Soil Sampling: Three different sampling locations were identified and the then cleared of leaf litter and vegetation. Using a hand trowel, a 10 cm depth hole was dug in the first location and the soil from the hole put in a collection container and well libelled. Excess soil was put back in the hole. This procedure was repeated with two other holes within the same location to obtain three samples from each of the three identified locations. The table below indicates the location where the samples were collected: Table 1: Sampling Details Sample No. Sampling location 1 Near the lake 2 Engineering school 3 Physical Sciences school The figure below shows a picture of the soil samples collected after sampling. Figure 1: A picture of three soil samples collected (three replicates for each sample) with labels indicating the location of sampling. Nutrient extraction: A single soil extract was prepared for each sample replicate, totaling to 50 mL. for each of the three samples for analysis. Three- 10 mL centrifuge tubes labeled a, b and c respectively with replicates from sample 1 were collected and 1 g of soil was accurately measured from each replicate of sample 1 and filled in the centrifuge tubes according to the labels. 10 mL of demineralized water was added in each of the tubes and vigorously shaken for about 5 minutes. The samples were then mounted on a centrifuge at 3,000 rpm for about 10 minutes before combining the supernatant of each tube into a larger tube of 50 mL to make one extract for sample 1, totaling to 30 mL. The steps highlighted above were repeated for sample 2 and 3. Below is a picture taken for samples prepared ready for chemical analysis. Figure 2: A picture of soil samples prepared ready for analysis Nutrient, Salinity and pH Measurements: After preparations in the steps above, 5 mL of each supernatant sample was transferred into a 50 mL tube by use of a micropipette and then diluted to the 50 mL mark using demineralized water. Using a pH meter and conductivity meter, the pH and salinity of the 50 mL diluted extract were measured respectively. The remaining undiluted sample extracts were then used to conduct nutrient measurements after filtering through a 0.45 µm nylon using a syringe into a 50 mL tube. The measurements were then recorded in a table. Results and Discussion Soil colour is one of the physical properties commonly used to describe soil. It enables one to know some of the soil’s characteristics, such as soil processes, mineral composition, age, etc. Soil samples collected at the Engineering school show a strong brown colour with gravelly fragments that are clearly suspended in water. Soils sampled near the lake are dark grey in colour. They have medium sized gravels and form a clear suspension in water. Soils collected at the Physical Sciences school also have a dark grey colour with coarse sand that also forms a clear suspension in water. All the soil samples have a fresh earthly smell. The following tables show the results of the measurements of the pH, salinity and nutrients taken during the lab. Table 2: pH measurement results Sample Reading (1) Reading (2) Reading (3) Average 1 6.77 6.96 6.46 6.73 2 6.16 6.20 6.22 6.19 3 6.74 6.57 6.56 6.62 From the table above, soil sample 2 from the Engineering school exhibit a pH value between 6.1 and 6.5, indicating that the soil is slightly acidic. Sample 1 and 3, from near the lake and Physical Science school respectively, have a pH range between 6.6 and 7.3, indicating that these soils are neutral. Table 3: Salinity measurement results Sample Reading (1) Reading (2) Reading (3) Average 1 22.78 22.17 22.04 22.33 2 8.33 8.38 9.21 8.64 3 17.56 17.28 17.08 17.31 From table 3 above, the soil samples collected near the lake shows excessively high salinity that is above 16 mmhos/cm. This may be an indication that the water in the lake is highly saline and due to intrusion into nearby land causes this high salinity in the surrounding soils. It is closely followed by the soil collected at the Physical science school that is also highly saline. The soil sample from the engineering school has a salinity range between 8 and 16 mmhos/cm, which can be described as high. Only salt tolerant plants can grow on these soils. Table 4: Nutrient analysis Sample Phosphate MB Nitrite NeD Ammonium InD Nitrate NeD 1 3.0 0.05 0 1 2 4.0 0.1 0.2 2 3 1.0 0 0.1 10 The table above shows the results of nutrient analysis of the three soil samples for Phosphate, Nitrite, Ammonium and Nitrate. In testing of Phosphorus using the Bray’s method, the soil extract is shaken with a solution of NH4F in HCl, which then dissolves the fraction of Phosphorus available in the soil. Complexes of Ammonium Fluoride with Fe and Al trivalent ions in the acid consequently release the Phosphorus held in the soil. The reactions taking place are represented by the equations shown below: 3 NH4F + 3 HF + AlPO4 → H3PO4 + (NH4)3AlF6 3 NH4F + 3 HF + FePO4 → H3PO4 + (NH4)3FeF6 According to the Bray’s method, P range between 0 and 15 ppm is considered very low (Tan). All the samples fall within this range, even though there is slight difference for each sample due to different sampling locations. Nitrates and nitrites are extracted from a soil sample by shaking the soil in a 0.01 M CaSO4 followed by filtration. The nitrate is reduced to nitrite, which then reacts with sulfanilamide in acidic conditions to form a diazo compound. The diazo compound couples with N-1-Napthylethylenediamine dihydrochloride to form a purple dye. The same process is used to determine nitrite. The nitrite and nitrate levels in the soil samples are very low. Sample 3 shows a relatively high level of nitrate compared to sample 1 and 2. Again, this difference may be attributed to the different locations of sampling. Ammonia is extracted by shaking a sample of the soil with 2M KCl. The ammonia reacts with salicylate in the presence of a catalyst (nitroprusside) to form a green complex. Levels of ammonia below 15 ppm in a given soil is considered to be very low, which is the case for all the soil samples in this experiment. The amount of nutrients available is an indication of the soil’s capacity to supply these nutrient to plants, and is also important in developing nutrient fertility classes for fertilizer recommending schedules (David Davidescu). This experiment can be improved by increasing the number samples in every location, the larger the sample size, the more accurate results will be obtained. Also, using thoroughly dried samples will help to eliminate positive interferences by N nitrite in the determination of Nitrates and nitrites. Conclusion This experiment provides a good learning experience on soil sampling and laboratory analysis of soils. Sample 2 is slightly acidic while sample 1 and 3 are neutral. All the samples recorded high levels of salinity, with very low levels of nutrient elements. References Read More