Question

Appu’s father wants to grow onions on his farm. Appu’s farm has three kinds of soil in different areas. Onions grow best in loamy soil. So, Appu decided to measure the percolation rate for the three different soils on his farm. He used a device like the one shown below. Appu, however, forgot and added different quantities of water while testing the percolation rate for each soil. He measured the time taken for all the water added to the device to percolate and tabulated them.

$\begin{array}{ccc}\text{Soil Number}& \text{Quantity of water added}& \text{Time taken to percolate completely}\\ \text{Soil 1}& \text{500 mL}& \text{300 minutes}\\ \text{Soil 2}& \text{200 mL}& \text{30 minutes}\\ \text{Soil 3}& \text{100 mL}& \text{300 minutes}\end{array}$

Which soil must be used to grow onions?

• A. Soil 1
• B. Soil 2
• C. Soil 3
• D. None of the above

Answer 1

The correct option is A

Soil 1

Different types of soil have different percolation rates. Sandy soils have the highest while clayey has the lowest. Loamy has a percolation rate in between. (Remember that larger the soil particle size, higher the water percolation rate).

Percolation rate = $\frac{\text{Anount of water percolated(mL)}}{\text{Time taken(minutes)}}$

Using this formula we can find the percolation rates as below:

$\begin{array}{cccc}\text{Soil Number}& \text{Quantity of water added}& \text{Time taken to percolate completely}& \text{Percolation rate}\\ \text{Soil 1}& \text{500 mL}& \text{300 minutes}& \frac{500mL}{300min}=1.67mL/min\\ \text{Soil 2}& \text{200 mL}& \text{30 minutes}& \frac{200mL}{30min}=6.67mL/min\\ \text{Soil 3}& \text{100 mL}& \text{300 minutes}& \frac{100mL}{300min}=0.33mL/min\end{array}$

Thus the order of percolation rate is:

Soil 2>Soil 1>Soil 3

As stated before, loamy soils have percolation rates in between sandy and clayey soils. Thus, Soil 1 is loamy and is suitable for growing onions.