To determine the gross depth of irrigation required to bring soil moisture content to field capacity, we can follow these steps:

Step 1: Calculate the soil's available water content (AWC)

The available water content is the difference between the moisture content at field capacity (FC) and the wilting point (WP).

$AWC = FC - WP = 32\% - 12\% = 20\%$

Step 2: Determine the amount of water to be replenished

Since irrigation is applied when the available soil water reduces to 60%, the remaining soil water is 40%. Therefore, we need to replenish 60% of the available water content:

$\text{Water to be replenished} = 60\% \times AWC = 0.60 \times 20\% = 12\%$

Step 3: Calculate the net irrigation depth (d_net)

The net irrigation depth is the amount of water needed to bring the soil moisture to field capacity. This can be calculated using the formula:

$d_{\text{net}} = \text{Water to be replenished} \times \text{Bulk density} \times \text{Root zone depth}$

Given:

• Water to be replenished = 12% = 0.12
• Bulk density (BD) = 1.5 g/cm³
• Root zone depth (RZD) = 50 cm

Thus,

$d_{\text{net}} = 0.12 \times 1.5 \times 50 = 9 \, \text{cm}$

Step 4: Calculate the gross irrigation depth (d_gross)

The gross irrigation depth accounts for field water application efficiency. Since the application efficiency is 75%, we can calculate the gross irrigation depth as:

$d_{\text{gross}} = \frac{d_{\text{net}}}{\text{Application efficiency}} = \frac{9}{0.75} = 12 \, \text{cm}$

Thus, the gross depth of irrigation required is 12 cm.

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Do you need further clarification or more details?

Here are 5 related questions:

1. How does root zone depth affect irrigation requirements?
2. What is the significance of the wilting point in soil moisture management?
3. How can you improve field water application efficiency?
4. What factors affect the bulk density of soil?
5. How does irrigation frequency relate to available water content?

Tip: Understanding soil water retention characteristics can help optimize irrigation scheduling for better crop yield and water conservation.