Sampling Soils in a Heterogeneous Research Plot

This method can help improve the experimental rigor in a soil sampling procedure. Such as, the sample size required for soil sampling and associated accuracy. The main advantage of this technique is that it provides a quantitative way to sample soils and two, to balance the research needs and resource availability.

The implications of this technique extend towards research plots and various shapes, areas and locations because the statistical power analysis method remains the same. Demonstrating the procedure will be Siyang Jian, a graduate student from my laboratory. Identify sampling zones within a research plot.

Then, determine the number of square grids with equal length. Based on the size and shape of the research plot, the target number of square grids is expected to be between 6 and 10. So that the total number of soil samples is controlled below 30 within a plot.

Mark the center of each square grid, or centroid, and create a circular sampling area with a diameter equal to the side length of the square grid. Stand on the centroid in the circular zone with closed eyes and throw a small stone in a random direction and distance from the centroid. If the stone is dropped outside of the circular area, do it again until the first sampling location is identified.

Put a flag on the sampling location and number the flag. Repeat this step until 3 random sampling locations are obtained in the circular zone. Then, repeat these steps in all other circular sampling zones until all locations are determined, and numbered, in a sequential order.

Choose one corner point and identify it as the origin for the sampling area in the plot. Measure horizontal and vertical distances of each flag location relative to the origin. After that, record the distances in a field notebook as x and y coordinates.

Use a soil auger to a take soil core from each flagged location and label the bag based on the flag number. Repeat this step until soil cores are taken at all flagged locations. To minimize the influence of sampling, ensure that the bags containing the soil samples stay within their respective flag until the end of the collection, when all bags in the plot should be assembled at once.

Transport the soil samples in coolers to the laboratory and process each soil core on the same day. Once in the laboratory, remove roots from each core and sieve the core through a 2mm soil sieve. Proceed to thoroughly homogenize each core sample prior to any analysis.

To determine soil moisture content in each sample, first oven dry sub samples for 24 hours at 105 degrees celsius. Then, ground the air dried soil sub samples to a fine powder for a total carbon analysis. To obtain the soil organic carbon, or SOC, weigh each soil sub sample in an open vessel using a microbalance.

Then, load the open vessel in an elemental analyzer. To quantify the soil microbial biomass carbon, or MBC, first weigh fresh fumigated and non-fumigated soil sub samples. Then, add 1ml of chloroform to the fumigated soil sample only.

Also, add 25ml of potassium sulfate to the non-fumigated soil sub sample. After 24 hours, add 25ml of potassium sulfate to fumigated samples. After shaking each tube for one half hour, collect the soil extract by passing the solution through a Whatman number 4 filter paper.

Now, add 5ml of soil extract and 5ml of persulfate reageant to two tall culture tubes. Cap the tubes tightly and place them in the drying oven at 85-90 celsius for at least 18 hours, but no more than 24 hours. Remove the tubes from the oven carefully, and cool to room temperature before analyzing.

Combine the SOC and MBC data set with x and y coordinates based on the flag numbers in the plot. Finally, obtain the coefficient variation and create the plot based on this equation. Representative results of both SOS and MBC are shown here.

A total of 9 centroids and 27 sampling points are determined for SOC. In order to achieve the same sampling accuracy, the sample size requirements for SOC are generally higher in hardword and pine forest soils, as compared to cultivated soils. Shown here is the sample size requirement in each soil type to achieve a sampling error under 10%A total of 8 centroids and 24 sampling points are determined for MBC.

In order to achieve the same sampling accuracy, the sample size requirements for MBC are generally higher in fertilized soils, than that in unfertilized soils. While attempting this procedure, it's important to remember to apply these plots to meet the future sampling as it allows you to derive the number of soil samples to meet your research needs and the desired sampling accuracy. After its development, this technique paves the way for researchers in a field of soil ecology to explore spatial characteristics in other soil nutrients and about new chemical features.