For this activity you will estimate and calculate the available water holding capacity of a soil using properties of structure and texture.
Step 1: Observe the range soil profile set out by your instructor. Determine the structure of each soil horizon using your red field guidebooks. Using the figure below, correlate the structure determined for each horizon to the rate of infiltration. Select the dominant rate of infiltration as your final estimate.
Step 2: Determine the texture for each soil horizon within the range soil profile. Based on your results and the relationship of texture and infiltration (which you just learned in Activity 3), what do you estimate the available-water holding capacity will be, (circle one of the following options on the following page):
The available water classes are:
- Very low. Up to and including 7.5 cm of water
- Low. Greater than 7.5 cm but less than or equal to 15.0 cm of water
- Moderate. Greater than 15.0 cm but less than or equal to 22.5 cm of water
- High. Greater than 22.5 cm of water
Step 3: You will now calculate the available water holding capacity of your soil using your predetermined textures, the depths of each horizon, and the following information on coarse fragments provided below. Use Table 2 provided in the soil-water relations section to determine the calculation factors for each soil texture. Calculate the water holding capacity according to instructions provided in the text above, and assume that the depth boundary of the last horizon is 150 cm.
|Horizon||Depth||Texture||Available water calculation factor||% Coarse fragment in horizon|
Using the information in the table above, calculate your available-water to a depth of 150 cm for this range soil and using your final answer determine the final available-water class of this same soil:
Available-water calculated for soil profile = ________________________
Available-water class = ________________________
- Do your estimated infiltration rates and calculated available-water holding capacity make sense together? Please explain the relationship between the two, and why or why not they make sense together.
- Did your estimated available-water holding capacity match your calculated available-water holding capacity? If not, where could you have assumed or calculated incorrectly?
- Based on your final calculation would plants grow well in this soil? Why or why not?