How do I read a soil texture diagram and determine the texture class for a soil sample with 50% sand, 20% clay, and 25% silt?

The diagram is a ternary plot with three axes representing the percentages of sand, clay, and silt.

• % Sand is read along the bottom axis, with lines running diagonally upwards to the left.
• % Clay is read along the left axis, with lines running horizontally to the right.
• % Silt is read along the right axis, with lines running diagonally downwards to the left. The sum of the percentages of sand, clay, and silt for any soil sample must equal $100\%$.

a) Sample A: $50\%$ sand, $20\%$ clay, $25\%$ silt
First, check if the percentages sum to $100\%$: $50\% + 20\% + 25\% = 95\%$. This sum is not $100\%$. Assuming there's a typo and the silt percentage should be $30\%$ to make it $100\%$, or that the question implies the given values are approximate and we should use them as is. Given the context of soil science, it's highly likely the sum should be $100\%$. Let's assume the question intends for the sum to be $100\%$ and there's a slight error in the silt value, or that the values are to be plotted as given and the closest region identified.
Let's re-evaluate the sum: $50\% \text{ sand} + 20\% \text{ clay} + 25\% \text{ silt} = 95\%$.
This is a common issue in these types of questions. If we strictly follow the given numbers, we plot $50\%$ sand, $20\%$ clay, and $25\%$ silt.

• Find $50\%$ on the sand axis (bottom, reading right to left). Follow the line diagonally up-left.
• Find $20\%$ on the clay axis (left, reading bottom to top). Follow the line horizontally right.
• Find $25\%$ on the silt axis (right, reading top to bottom). Follow the line diagonally down-left. The intersection of these three lines falls within the region labeled sandy clay loam.

b) Sample B: $40\%$ sand, $50\%$ clay, $10\%$ silt
Check sum: $40\% + 50\% + 10\% = 100\%$. This is a valid sample.

• Find $40\%$ on the sand axis. Follow the line diagonally up-left.
• Find $50\%$ on the clay axis. Follow the line horizontally right.
• Find $10\%$ on the silt axis. Follow the line diagonally down-left. The intersection of these three lines falls within the region labeled clay.

c) Sample C: $94\%$ sand, $3\%$ clay, $2\%$ silt
Check sum: $94\% + 3\% + 2\% = 99\%$. This is also not exactly $100\%$. Similar to sample A, we will plot the given values.

• Find $94\%$ on the sand axis (very close to $90\%$ and $100\%$). Follow the line diagonally up-left.
• Find $3\%$ on the clay axis (very close to the bottom). Follow the line horizontally right.
• Find $2\%$ on the silt axis (very close to the bottom right). Follow the line diagonally down-left. The intersection of these three lines falls within the region labeled sand.

1.1.1 The texture classes are:

a) Sample A: sandy clay loam

b) Sample B: clay

c) Sample C: sand

a) Suitable for pottery work in rural communities
Pottery requires soil with high plasticity and ability to hold shape, which is characteristic of soils with a high clay content. Sample B is clay, which is highly suitable for pottery.

b) Most suitable for cultivation
The most suitable soil for cultivation is typically a loam, which has a balanced mix of sand, silt, and clay, providing good drainage, water retention, and nutrient availability.

• Sample A (sandy clay loam) has a good balance and is generally fertile.
• Sample B (clay) can be too heavy, poorly drained, and difficult to work.
• Sample C (sand) drains too quickly and has poor nutrient retention. Therefore, Sample A (sandy clay loam) is the most suitable for cultivation among the given options.

1.1.2 The samples that apply are:

a) Suitable for pottery work in rural communities: Sample B

b) Most suitable for cultivation: Sample A