Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): The water budget in the field is accounting the inputs and outputs of water and also considers the volume of water present in the field.
Reason (R): The main governing factor in field water budget is the stored soil moisture.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

The field water budget is a simple conservation of mass equation: \(\text{Inputs} - \text{Outputs} = \Delta \text{Storage}\).
The soil profile acts as the storage reservoir, and the moisture level in this reservoir governs all water movement rates.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A field water budget (or water balance) is an accounting system used to track the movement of water into and out of a specific soil-crop root zone over a given period.
This system is based on the law of conservation of mass, stating that the change in water storage must equal the difference between total water inputs and outputs.

Step 2: Detailed Explanation:
Let us analyze both statements and their relationship:
- Assertion (A): The field water budget equation is represented as:
\[ \Delta S = (P + I + CR) - (ET + RO + DP) \]
where \(P\) is precipitation, \(I\) is irrigation, \(CR\) is capillary rise (inputs); \(ET\) is evapotranspiration, \(RO\) is surface runoff, \(DP\) is deep percolation (outputs); and \(\Delta S\) is the change in stored soil moisture.
Since this equation accounts for all water inputs, outputs, and the remaining water volume within the field root zone, Assertion (A) is correct.
- Reason (R): The central term that balances the inputs and outputs in the water budget is the stored soil moisture (\(S\)).
The soil acts as a physical water reservoir.
The amount of soil moisture stored in the root zone dictates the rate of evapotranspiration, controls the infiltration rate of irrigation and rainfall, and determines how much excess water will be lost to runoff or deep percolation.
Thus, stored soil moisture is the primary governing factor that regulates the entire water balance system in the field.
Therefore, Reason (R) is correct, and it serves as the correct explanation for Assertion (A) by showing how the stored soil moisture acts as the regulating factor that balances all water inputs and outputs.

Step 2: Final Answer:
Both (A) and (R) are true and (R) is the correct explanation of (A).